Apip

Scopus Publications

Evaluation of Lake Toba's water level decline in Indonesia over the past six decades
Mohammad Syamsu Rosid, Hendri Irwandi, Apip, Terry Mart, Raden Dwi Susanto, and Albertus Sulaiman
Elsevier BV

Trend analysis of extreme rainfall in Cikapundung Watershed, West Java, Indonesia
Unggul Handoko, Muh Fakhrudin, Apip, Hidayat, Turmudi, and Endra Triwisesa
EDP Sciences
Bandung is one of the areas prone to flood disasters in Indonesia. The areas frequently affected by flooding are located around the Cikapundung Watershed. Floods are triggered by several factors, namely: rainfall, changes in land use, as well as geological and morphological conditions. The aim of this research is to analyze rainfall in the Cikapundung watershed to see whether there is an increase in extreme rainfall from 1977- 2022. The method used in this research is first to test the homogeneity of rainfall over 45 years. Next, the extreme rainfall indices and the trend of each wet extreme rainfall indices were calculated using the Mann-Kendall test. The research results show that statistically, of the 20 indices analyzed, only one indices experienced a significant downward trend, namely the Rx5day indices at Kayu Ambon station. Other indices show a p-value of more than 0.05, which means statistically there is no trend, either an upward trend or a downward trend.

Assessment of soil erosion severity zones for prioritization of sedimentation control measures at Mahakam Cascade Lake in East Kalimantan, Indonesia
Apip and M Fakhrudin
IOP Publishing
Abstract Because of high sedimentation, Mahakam Cascade Lake’s sustainability functions are at risk. Surface soil erosion in its internal catchment area (51,571 km2) is the primary source of sediment. In order to control erosion, it is necessary to choose high-priority areas. This research aims to develop priority control zones based on the level of soil erosion in the lake’s catchment area. The distributed simulation model for rainfall, runoff, and sediment served as the main methodology to accomplish this. The model’s output includes spatial information on the five classes of soil erosion rates (very light, light, medium, heavy, and very heavy). We then establish the priorities for erosion control areas based on the erosion rate criteria. We determined that an area meeting the criteria for a very heavy erosion rate class (> 250 tons/ha) is the primary control priority within the catchment. The mapping results show that 26 sub-districts and 4 regencies administratively distribute the main control priority area. Each sub-district has a different total area for priority areas, and there are 8 sub-districts with a combined potential priority area of more than 300 km2. In general, mapping soil erosion severity zones can serve as a guide for more effective erosion control.

Monitoring tools to support ecosystem restoration: Insight from limited data in a floodplain area
M Yulianti, Apip, and D Verawati
IOP Publishing
Abstract Generally, the importance of monitoring tools in watershed management, particularly ecosystem restoration strategies, has been widely recognized. However, fewer studies have been conducted in areas with limited data. This study aimed to describe the effectiveness of restoration-associated projects linked to monitoring plan-based. First, we used a literature review to analyze various restoration projects developed in some countries. In most cases, the key to successfully implementing restoration strategies involves continued pre- and post-monitoring data. Next, we discuss a case study of developing restoration approaches in a floodplain area of the Batanghari watershed, Sumatra, Indonesia, with more data availability necessary. Our results highlighted that spatiotemporal analysis based on long-term hydrological data is one of the essential baselines required for sustainability management. Several improvements related to monitoring approaches need to be conducted in the Batanghari watershed, including an increase in the number of representative monitoring, time frames of monitoring (continuous and seasonal basis), automatization of monitoring methods, and strengthening community participation in monitoring through citizen science. To conserve or restore floodplain ecosystems, monitoring should be an essential component of the restoration strategies plan that needs to be integrated with the decision-making process in the context of watershed scale.

Daily variation of total suspended solid, total nitrogen, and total phosphorus at Cisangkuy River Basin, the Upper Citarum sub-Basin
S Aisyah, L Subehi, Apip, and D Verawati
IOP Publishing
Abstract The Cisangkuy basin is part of the upstream Citarum sub-basin, which flows through the Bandung regency’s. total suspended solid (TSS), nitrogen (N), and phosphorus (P) in the Cisangkuy River are potentially polluted due to human activities like agriculture. This study aims to reveal the daily trend of total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP) at the Cisangkuy River, the upper Citarum in the period of March-May 2023. The study was conducted from March to May 2023 in the Cisangkuy sub-basin. The measured water quality parameters included total suspended solids, nitrogen, and phosphorus. Data were analyzed visually and statistically using MS Excel 2013. From the results of observations at rainfall observation stations, the intensity of rain at the study location tends to be low to moderate (0.5- 50 mm), with the highest intensity occurring in early May. Generally, this pattern is followed by the values from observations of water level TSS concentration at Lamajang and Kamasan tended to follow the rainfall pattern with concentration values that exceeded standard water quality criteria for river. TP concentrations followed the TSS pattern relatively with concentrations exceeding standard water quality criteria during some of the study period. TN concentrations at both study locations showed high value and still met the standard criteria. Water pollution control should be prioritized based on crucial characteristics that contribute significantly to pollution in the Cisangkuy basin.

Development of Decision Support System (DSS) for surface runoff and erosion control structures planning: A case study in the Upper Citarum Watershed & towards sustainability inland waters ecosystem
Apip, L Subehi, M Fakhrudin, G Lee, S Aisyah, H Wibowo, D Verawati, A Hamid, and A Nurhidayat
IOP Publishing
Abstract The watershed ecosystem is a complex system in which there are numerous transportation and transfer mechanisms of mass and energy. To make management more effective in all national critical watersheds, there needs to be more scientific, evidence-based policymaking that is based on an understanding of the system and mechanisms of the socio-hydrological processes of the watershed. The availability of Decision Support System (DSS) technology can be the appropriate approach to this need because DSS can be an interface between scientific and practical needs (easy-to-use, easy-to-access, user-friendly). However, the availability and implementation of DSS as an important tool in the optimal design of sustainable watershed management in Indonesia are still very limited. This study aims to create a prototype DSS that practitioners and policymakers can use to identify priority areas and optimize technical solutions for controlling surface runoff and soil erosion at various scales in the internal watershed. Herein, the spatial-based numerical modeling system and process mechanism; the database and knowledge; and the Graphical User Interface (GUI) are the three main components that have been used as a framework for model-based DSS development. A distributed rainfall-runoff-erosion model (EcoHydro) is the main engine of DSS for spatially quantifying dimensions of hydrological responses, erosion rate, and sediment production according to the user’s specifications and providing design options for control measures of them. The upper Citarum river basin in West Java, which is a critical and first national priority watershed, has been selected as the case study for DSS development and to demonstrate its application. Furthermore, the resulting DSS can later be developed for use in watersheds and other nationally critical lakes.

Comparison of the application of HBV and HEC-HMS hydrology models for accessing climate change in the upper Citarum Watershed, Indonesia
Widya Ningrum, Apip, and Ida Narulita
IOP Publishing
Abstract Hydrologically, the upper Citarum watershed was critically damaged. This study propose to compare HBV and HEC-HMS model performance for estimating discharge in upper Citarum watershed. Besides, this study wants to know changes in discharge in the future as a result of climate changes. Discharge simulation was carried out with the HBV and HEC HMS models in the period 2006-2007 as calibration and 2008 as validation. Meanwhile, future discharge changes are calculated in 2045 based on climate model projections output from CORDEX namely MPI, CNRM, EcEarth, and CSIRO. Model performance is calculated based on the value of statistical bias, NSE, and correlation. The results showed that HEC-HMS model has bias, NSE, and corellation value of 6.33, 0.57, and 0.8. Whereas, the HBV values are 3.67, 0.61, and 0.76. Therefore, based on NSE and bias value, the HBV model performs slightly better than the HEC-HMS in upper Citarum watershed. There are an increase in the daily discharge by RCP4.5 scenario. In contrast, the daily discharge by RCP8.5 decreased in upper Citarum.

Effect of climate change to characteristic of extreme rainfall over Batanghari watershed
Unggul Handoko, Rizaldi Boer, Edvin Aldrian, Misnawati, Bambang Dwi Dasanto, and Apip
IOP Publishing
Abstract Climate change will cause extreme rainfall, both wet and dry. Extreme rainfall will cause catastrophic floods and droughts. Therefore, it is important to analyse extreme rainfall and flood events in the future. Disasters and environmental issues in the Batanghari watershed include flooding, drought, forest and land fires, sedimentation, and water quality degradation. Therefore, the Batanghari watershed is selected as a study area in this research. Research on climate change in the Batanghari watershed is crucial to understanding the trend of extreme conditions now and in the future. Characteristics of extreme rainfall will be analysed using the climate index that was developed by the Expert Team on Climate Change Detection and Indices (ETCCDI). Results show that climate change in the Batanghari watershed is indicated by increasing 5 of 6 extreme rainfall indices: R95p, R99p, Rx1day, Rx5day, and SDII. An increase in extreme rainfall is correlated with an increase in flood events in the Batanghari watershed in similar periods. The extreme rainfall index that most influences flooding in the Batanghari watershed is PRCPTOT and R99p. Flooding is expected to occur more frequently in the future than it does now. The Batanghari Hilir Sub-watershed is more vulnerable to extreme flooding in the future than other sub-watershed.

Hydrological characteristics of Mahakam cascade lake as a reference for the sustainability management
M Fakhrudin, Turmudi, F Setiawan, Apip, and Mislan
IOP Publishing
Abstract Mahakam cascade lakes consist of Lake Semayang, Melintang, and Jempang is a floodplain lake. Mahakam cascade lakes include the 15 national priority lakes which are the most urgent situation. This lake is characterized by dynamic water level fluctuation, resulting in high fishery productivity. The lake’s hydrological characteristic is the main component in controlling the lake ecosystem, therefore it is crucial to evaluate the influenced factors. The objective of this research is to describe the lake’s hydrological characteristics, including inlet-outlet discharge, sedimentation, water level pattern, and land cover change in the catchment area. Further, provide a reference for the conservation of lake ecosystems. We performed a field campaign to measure river discharge and collect water samples for sediment-load laboratory analysis. We analyzed daily water level data recorded from 1989 to 2010. We obtained the time series land cover from Landsat data and performed GIS spatial analysis. Our results revealed that first, the Rebak Rinding River has the biggest contribution to lake sedimentation (3,859 tons/day, 77% of the total sediments entering the lake). Second, the water level tended to increase during the medium and extreme flood seasons. Contrary, a relatively small decrease in the water level during the medium-receding season. Third, the catchment area is 51,573 km2 (66 times larger than the lake water bodies). From 2000 to 2019, the forest decreased by 2,063 km2. As a consequence, increased erosion-sensitive area by 2,695 km2. We emphasized preserving the catchment area is vital to reduce the sedimentation rate and water fluctuation. We recommend the Rebak Rinding sub-catchment as the priority area for controlling deforestation, and erosion on the plantation, mining, and agricultural area.

Physico-chemical properties and pollution status of the rivers at Konaweha watershed, Southeast Sulawesi
S Aisyah, A B Santoso, Apip, H Wibowo, and D Verawati
IOP Publishing
Abstract The Lasolo - Konaweha watershed is a river area in Southeast Sulawesi, Indonesia. It is a source of water for various sectors including irrigation and non-irrigation needs, and functions as a source of drinking water for several communities and industries. However, population growth and human activities have led to water quality degradation in the area. Many methods of determining water quality status have been developed, one of them is the pollution index (PI) method. The purpose of this study was to evaluate the characteristics of physico-chemical and determine the pollution status of the Lasolo – Konaweha watershed. The study utilized secondary data from the Hydrology and Water Quality Unit of the Sulawesi IV River Basin Center in Kendari, collected in 2020. The water quality data were analyzed according to the Government Regulations of Republic Indonesia No. 22 of 2021, and the pollution status was determined using the pollution index (PI) method. The water quality data were compared spatiotemporally using analysis of variance (ANOVA). The study found that several parameters were outside the water quality standards, including pH, total suspended solids (TSS), dissolved oxygen (DO), chemical oxygen demand (COD), methylene blue active substances (MBAS), and phenol. These parameters indicated a moderate to heavily polluted status for the Lasolo - Konaweha watershed. The study also found a strong correlation between water discharge and conductivity.

Aesthetics 3D geovisualization for flood disaster based on the XYZ coordinate

Land Ocean Connectivity Through Inland Water Ecosystem: A Coremap-CTI Project in The Coastal Area of Kendari Bay, Southeast Sulawesi
A B Santoso, Apip, H Wibowo, and S Aisyah
IOP Publishing
Abstract Coastal zone is highly valued ecosystem exposed to multiple and often cumulative natural and anthropogenic stressors such as catchment loads of nutrients and sediment, as well as climate warming. High loads of nutrients and sediment from the hinterland are dispersed into this zone leading to an increase microalgae community in which it may reduce light availability for corals and seagrasses. In this paper, we present the progress of our study in the coastal area of Kendari, Southeast Sulawesi, under the COREMAP-CTI Research Programme. Through such programme we are 1) investigating the flux of materials from the river basin to the marine environment, 2) characterising the key process that governing those fluxes, 3) developing models that capable of in predicting material fluxes under current and future environment (e.g., land-use and climate change). To do so, we integrate data and information derived from field observations and satellite imagery analysis to feed the developed rainfall-sediment-runoff and coastal ecological-hydrodynamic model. Not only focusing on the science of physical-biogeochemical processes of land-ocean interaction, the outcome of this research project is also aimed to support the development of adaptation strategy in combating climate change and anthropogenic pressure in the near future of coastal ecosystem.

Impact of climate change on flood inundation in a tropical river basin in Indonesia
Kodai Yamamoto, Takahiro Sayama, and Apip
Springer Science and Business Media LLC
AbstractClimate change will have a significant impact on the water cycle and will lead to severe environmental problems and disasters in humid tropical river basins. Examples include river basins in Sumatra Island, Indonesia, where the coastal lowland areas are mostly composed of peatland that is a wetland environment initially sustained by flooding from rivers. Climate change may alter the frequency and magnitude of flood inundation in these lowland areas, disturbing the peatland environment and its carbon dynamics and damaging agricultural plantations. Consequently, projecting the extent of inundation due to future flooding events is considered important for river basin management. Using dynamically downscaled climate data obtained by the Non-Hydrostatic Regional Climate Model (NHRCM), the Rainfall-Runoff-Inundation (RRI) model was applied to the Batanghari River Basin (42,960 km2) in Sumatra Island, Indonesia, to project the extent of flood inundation in the latter part of the twenty-first century. In order to obtain reasonable estimates of the extent of future flood inundation, this study compared two bias correction methods: a Quantile Mapping (QM) method and a combination of QM and Variance Scaling (VS) methods. The results showed that the bias correction obtained by the QM method improved the simulated flow duration curve (FDC) obtained from the RRI model, which facilitated comparison with the simulated FDC using reference rainfall data. However, the high spatial variability observed in daily and 15-day rainfall data remained as the spatial variation bias, and this could not be resolved by simple QM bias correction alone. Consequently, the simulated extreme variables, such as annual maximum flood inundation volume, were overestimated compared to the reference data. By introducing QM-VS bias correction, the cumulative density functions of annual maximum discharge and inundation volumes were improved. The findings also showed that flooding will increase in this region; for example, the flood inundation volume corresponding to a 20-year return period will increase by 3.3 times. River basin management measures, such as land use regulations for plantations and wetland conservation, should therefore consider increases in flood depth and area, the extents of which under a future climate scenario are presented in this study.

Implementation of ecohydrology to support sustainable water resources management in tropical region, Indonesia
Ignasius D.A. Sutapa, Apip, M. Fakhrudin, and Herry Yogaswara
Elsevier BV

Water balance model aided in estimating net groundwater inflow at Lake Maninjau, West Sumatra - Indonesia
Apip, U Handoko, I Ridwansyah, AB Santoso, and L Subehi
IOP Publishing
Abstract Sustained lake functioning requires proper catchment land and water management. To address this, quantitative information and comprehensive understanding of the spatiotemporal dynamics and hydrological budget of the lake ecosystem are required. However, measuring hydrologic components such as groundwater discharge into a freshwater body is difficult, since its direct measurements are costly, time-consuming, and hardly implemented. Therefore, this study was intended to quantify groundwater inflow to the lake through an effective approach using the water balance modeling technique. Herein, groundwater discharge and contribution were calculated as the water balance residual in terms of net groundwater inflow. It can be considered a minimum estimate of groundwater inflow, as there the groundwater outflow maybe exists but not quantifiable. The approach has been applied for Lake Maninjau which is categorized as a deep, regulated, and tecto-volcanic lake located in West Sumatra Province, Indonesia. The result indicates that the groundwater inflow slightly moderately influences the fluxes of new water volume (the region between observed lowest and highest lake water level) at the upper layer of Lake Maninjau. Its contribution was equivalent to at least 20-28% according to the assessment for the years of 2013 and 2014. Annually, the new water volume recharged from the groundwater inflow corresponded to at least 182-281 million m3. Moreover, these findings enhance a previous study stated that the terrain system of Lake Maninjau is dominated by a rare groundwater aquifer.

Mapping of Mature and Young Oil Palm Distributions in a Humid Tropical River Basin for Flood Vulnerability Assessment
E M S Yamamoto, T Sayama, K Yamamoto, and Apip
IOP Publishing
Abstract Oil palm is one of the key drivers of economic growth in some regions in the humid tropical countries such as Indonesia. Previous studies show that floods risk at particular river basins in Indonesia will increase in the future due to climate change. This will give negative impacts to the sustainable production of palm oil in the future and subsequently the regions’ economy. Discussion on adaptation strategies on this matter is necessary however, the vulnerability of oil palm plantations against floods at river basin scale are still poorly understood. Field surveys for oil palms’ vulnerability at such scale is costly in time, labour and resources, and making use of remote sensing is more feasible. The aim of this study is to use remote sensing in assessing oil palm vulnerability against floods at river basin scale. To achieve this objective two oil palm distribution maps which were developed using Sentinel imageries for years 2015 and 2018 allowing young oil palms to be matured under normal condition. To understand the impact of floods to oil palms, a composite of flood extents using radar scenes for years 2016 and 2017 was developed. Our results show that young oil palms are highly vulnerable to floods compared to matured ones. Only 6% of the earlier could survived floods and be matured in time, while most of the matured ones could survive.

Analysis of Total Suspended Solid (TSS), nitrite, nitrate and runoff changes during rainfall events at River Kurambik, Lake Maninjau
L Subehi, I Ridwansyah, Apip, M Yulianti, A Dianto, and E T Wisesa
IOP Publishing
Abstract Lake Maninjau is a caldera lake with a volcano-tectonic type. The existing land management of Lake Maninjau catchment area influenced water quality, included River Kurambik as one of the rivers that flow into Lake Maninjau. It influenced degradation of water quality, nutrient enrichment and exceeded the carrying capacity. The source of pollutants, especially non-point sources pollution can be a point source in large numbers. For example, runoff from agricultural areas containing pesticides and fertilizers, runoff from residential areas (domestic). In order to gain insight into the effect of watershed conditions on water quality in Lake Maninjau, we statistically analyzed Total Suspended Solid (TSS), Nitrite, Nitrate, discharge, water temperature (Tw) and, air temperature (Ta) at River Kurambik, Lake Maninjau. Besides water level and water temperature (HOBO sensor), also Teledyne ISCO sampler equipment was used to take sample water for analysis. Some results showed the relation among parameters such as TSS, Nitrite, Nitrate, discharge, and water temperature as long as our observation in periods September – November 2018. Based on data, it could be explained that the seasonal variability of atmospheric conditions influenced fluctuations in air and water temperature nearly proportionally (R2 = 0,883). The change of discharge influenced Total Suspended Solid (TSS) significantly (R2 = 0,917). It indicated the land use change contributed to the water quality during rainfall events through runoff sediment and materials into the lake. On the other hand, Nitrite, Nitrate parameters seemed to have various changes during rainfall events. The land use management and economic values of these lakes and ecosystem should be elucidated. In order to maintain the sustainability of the lake, land cover management at the catchment area is also necessary for the next study.

Numerical model for quantifying the function of soil erosion and sediment transport controls at slope agricultural landsApip
IOP Publishing
Abstract The objective of this study was to build a numerical model that has the capability to account for the effect of various water and soil conservation practice scenarios in reducing erosion rate and sediment loads along slope cultivated lands. As further, inter-rill and rill erosion were implicitly represented by the raindrop and overland flow soil detachments. The observed surface runoff and sediment concentration data in response to incoming water from the rainfall within selected agricultural river catchments were used to evaluate the performance of spatially distributed, processed-based Hillslope Erosion and Sediment Transport Model (HESTM). As erosion and sediment yield from slope lands are primarily determined by rainfall, surface runoff, topography, vegetative canopy cover, ground surface cover, soil erodibility, and sediment properties. Thus, several scenario-based control strategies according to three clusters of water erosion and sediment control measures had been examined. They are agronomic measures and soil management; field management; and mechanical approach. Accordingly, scenario-based water and soil conservation practices were designed for setup numerical experiments of the model at selected water catchments located in the Upper Citarum and Cimanuk River basins, West Java which dominated by planted seasonal crops (carrot and potato). The study area was discretized into a spatial resolution of 30 x 30 m for considering heterogeneity and control measures function in rainfall-runoff-erosion-sediment process mechanisms.

Flood Hazard Assessment with High Spatial Resolution under Climate Change Scenario
Jazaul Ikhzan, Apip, M Fakhrudin, Luki Subehi, and Kodai Yamamoto
IOP Publishing
Abstract One of the important components in flood disaster risk reduction is the availability of spatial information on flood risk that include: (1) flood hazard component such as flood discharge ( q), flood depth (h), flood extent (A ), and flood duration (t), and (2) the loss value due to flood which could be quantified in the form of damage costs (θ). Change in the value of risk f (h, A, t, θ) was hypothesized to be sensitive to climate change and other environmental factors that exist at a river basin area. Therefore, it is quite important to control the flood disaster risk as a part of adaptation programs to the climate change impacts and to deal with the increasing pressure due to anthropogenic activities. Additionally, to support the action plan and to increase the understanding and awareness related to the flood disaster mitigation, spatial information on flood risk which having high resolution and precision is required. This study aimed to quantify the spatial information of flood hazard with high spatial resolution. Two Dimensional (2-D) flood-modelling system (e.g., rainfall-runoff-inundation) at the river basin scale has been used as the main method in quantifying the flood hazard dimension. Furthermore, this study was focused in the Batanghari River basin, Sumatra and 13 river catchments flow out through the Jakarta Capital City of Indonesia. Obtained hazard information forms the basis for long term management decisions on improving operational flood risk management, especially in order to cope with impacts of the future climate change.

Characteristics of soil and hillslope responses in humid tropical forests in sumatra, indonesia
Takahiro Sayama, Ryoko Araki, Kodai Yamamoto, and Apip
Japan Society of Hydrology and Water Resources
: Extensive deforestation in tropical regions may signifi‐ cantly influence the hydrological cycle. However, subsur‐ face runoff processes in thick soil layers in humid tropical forests are poorly understood; thus, the impact of land-use changes in such regions remains unclear. To understand runoff generation mechanisms in the humid tropics, we monitored groundwater and soil moisture dynamics in a forested hillslope in Sumatra, Indonesia. We also conducted field and laboratory experiments to determine soil hydraulic characteristics and used the results to simulate vertical infiltration and groundwater recharge. Although the soil is categorized as silty clay loam, the high infiltrability and high water retention capacity of the soil enabled infil‐ tration during storm events and recharge to groundwater. Within the 4–5 m thick soil layer at the foot of the hillslope, the shallow groundwater table quickly responded to rainfall and did not drop below a depth of 2–3 m, possibly due to continuous flow contributions from the upslope. Overall, this study demonstrates the importance of subsurface flow and vertical infiltration in thick soil layers in humid tropical regions.

Water balance of Maninjau watershed with SWAT hydrological model
I Ridwansyah, H A Rustini, M Yulianti, Apip, and E Harsono
IOP Publishing
Abstract Lake Maninjau was one of the international tourist destinations before the 2000s. Aside from being used as a source of 66 MW hydroelectric power built in 1972, currently, this caldera lake is also used for aquaculture. Lake Maninjau ecosystem, which consists of water bodies and watersheds, has an area of 23,729.3 Ha. The surface area of Lake Maninjau at +461.5 m asl is 9,737.5 Ha. Calculation of water balance in the Lake Maninjau watershed becomes a necessity because of its multi-functional status. Maninjau watershed water balance is estimated using SWAT (Soil and Water Assessment Tools) model. Rainfall data from Climate Hazard Group InfraRed Precipitation with Station (CHIRPS) was reanalyzed and compared with local rainfall data. The simulation conducted for 1981 - 2019 on the sub-watershed scale produced NSE and R2 values of 0.61 and 0.7, respectively. The simulation was scaled up for the entire catchment of Lake Maninjau. Simulation results showed that an average annual rainfall of 2,483.9 mm/year produced a surface flow, interflow, base flow, and recharge to aquifer of 7.8 mm/year, 1397.4 mm/year, 273.4 mm/year and 14.7 mm/year, respectively.

The impact of land use and climate change on surface runoff and groundwater in Cimanuk watershed, Indonesia
Iwan Ridwansyah, Meti Yulianti, Apip, Shin-ichi Onodera, Yuta Shimizu, Hendro Wibowo, and M. Fakhrudin
Springer Science and Business Media LLC

Studies of Carrying Capacity and Zonation at Menjer Lake, Central Java Using A Multidisciplinary Approach for Sustainable Utilization
L Subehi, M Fakhrudin, Apip, I Ridwansyah, G P Yoga, H A Rustini, O Samir, F Ali, A Wahyono, and S Suwardi
IOP Publishing
Abstract Tropical lake is one of the unique ecosystems which are functioning in both ecological and economic services. Telaga Menjer as a volcanic lake, has strategic values as a hydropower plant, tourism, agriculture, capture fisheries and floating net cages farming. It influenced a degradation of water quality and quantity, nutrient enrichment and exceed the carrying capacity. Telaga Menjer has a catchment area of around 2.27 km2 with a lake surface area of 0.61 km2.The purpose of this research is to investigate the characteristic of lake to know the carryng capacity and utilization zone with a multidisciplinary approach. For measuring its depth, the Hondex PS-7 portable depth sensor is used with a maximum depth of 80 m. The water quality parameters stratification were measured by logger version CTD profiler with a depth interval of 1 m on July 2019. The results showed that DO values were observed until the bottom of lake (45 m). Moreover, Total Nitrogen (TN) was very high concentration, indicating more fertilizer from agriculture. Meanwhile, lower concentration of pesticides were obtained. Next, the land use management, economic values and social carrying capacity of Talaga Menjer should be elucidated in order to maintain the sustainability of the lake.

Ensemble flood simulation for a small dam catchment in Japan using nonhydrostatic model rainfalls - Part 2: Flood forecasting using 1600-member 4D-EnVar-predicted rainfalls
Kenichiro Kobayashi, Le Duc, Tsutao Oizumi, Kazuo Saito, and
Copernicus GmbH
Abstract. This paper is a continuation of the authors' previous paper (Part 1) on the feasibility of ensemble flood forecasting for a small dam catchment (Kasahori dam; approx. 70 km2) in Niigata, Japan, using a distributed rainfall–runoff model and rainfall ensemble forecasts. The ensemble forecasts were given by an advanced four-dimensional, variational-ensemble assimilation system using the Japan Meteorological Agency nonhydrostatic model (4D-EnVar-NHM). A noteworthy feature of this system was the use of a very large number of ensemble members (1600), which yielded a significant improvement in the rainfall forecast compared to Part 1. The ensemble flood forecasting using the 1600 rainfalls succeeded in indicating the necessity of emergency flood operation with the occurrence probability and enough lead time (e.g., 12 h) with regard to an extreme event. A new method for dynamical selection of the best ensemble member based on the Bayesian reasoning with different evaluation periods is proposed. As the result, it is recognized that the selection based on Nash–Sutcliffe efficiency (NSE) does not provide an exact discharge forecast with several hours lead time, but it can provide some trend in the near future.

Comparison of runoff generation methods for land use impact assessment using the swat model in humid tropics
Eva Mia Siska Yamamoto, Takahiro Sayama, Kodai Yamamoto, and Apip
Japan Society of Hydrology and Water Resources
Hydrological responses due to deforestation in a humid tropical catchment were analyzed using two runoff genera‐ tion methods available in the Soil Water Assessment Tool (SWAT) model: the Curve Number (CN) and the GreenAmpt (GA) methods. The calibrated model, which per‐ formed well in simulating runoff under present land use condition in the Batanghari River Basin, Indonesia (42,960 km2), was then used to simulate runoff using past and future land use scenarios. Simulations showed similar changes in the annual water budget: decreasing evaporation and increasing total discharge. However, the two methods showed opposite changes in flow regimes: high flow increased (13%) under the CN while low flow increased (27%) under the GA. These results are associated with dif‐ ferences in runoff generation mechanisms, where surface runoff contributes to total discharge to a much larger extent under the CN (43%) than the GA (4%). Land use changes caused a reduction in infiltration rate, leading to higher high flow under the CN, while high flow did not change under the GA. Instead, lower evapotranspiration increased groundwater flow under the GA, and thus the steady low flow increased. This study suggests that the runoff genera‐ tion method should be selected carefully based on the dom‐ inant flow pathway of a catchment, particularly for land use impact studies in the humid tropics.

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