The purpose of this research is to create a model of the discharge as the impact of climate change due to global warming. The study was conducted using data from the Bangga watershed. Monthly water balance model used is the development of a model FJ. Mock by entering the natural phenomena that occur at this time such as climate change, canopy interception, rainfall distribution based on land use, soil type and soil characteristics. Calibration of water balance is used to determine the performance of the models to variations in climate change. Then, analysis is conducted as the effect of rain and temperature on runoff at river Bangga. The conclusion of this research were: 1) Accuracy of discharge simulation models against observed discharge is quite good, which is characterized by the Nash coefficient (Ns) close to one except for a few periods and annual rainfall runoff ratio (RE) approaches one. 2) Changes in rainfall have a considerable influence on the runoff, while the effect of temperature on runoff is not too significant.

Nowadays, water resources management development not only sees from the side of excess or lack of water in quantity, but already includes aspects of quality, health, aesthetics, comfort and environmental sustainability. The problems faced by urban areas are the disruption of activities due to flood events. The opportunities for flooding depend on climate and global weather behaviour. The magnitude of the flood depends on the rain with certain characteristic that is generally seen from the intensity and duration of rain events. While the magnitude of losses due to floods depends on the magnitude of the flood and the level of economic development of the region concerned. This paper discusses the importance of understanding the short duration of rain characteristics as well as its response to flood discharge plans in both micro and macro-depleting systems in urban areas. With this understanding, it is expected that handling actions at various levels of the disaster cycle can be well anticipated so that the negative impacts that may arise can be minimized. Characteristic analysis of short duration rainfall is done by looking at the pattern of hourly rainfall distribution occurring in several rainfall observation stations in Java Island. The Mononobe equation is used to see the level of compatibility of the rainfall distribution pattern with RMSE, NMSE and MAE score indicators. The analysis results show the reliability level of Mononobe equation for the hydrology analysis in the location which has no short duration rainfall data.

Java is the most populous island with the largest percentage of rice fields in Indonesia. However, rice fields in Java Island often experience water shortages, so an analysis of the potential water availability for irrigation in Java is required. This research aims to analyze water's potential to meet irrigation water needs in each catchment area in Java. In this research, the potential for irrigation water in Java is calculated based on the balance of water balance between water availability and DMI and Irrigation water needs. This research is divided into two parts: (1) analysis of water availability using the WFLOW hydrological simulation; and (2) water demand analysis based on population statistical data. Based on this research, it can be concluded that the water balance between water resources and irrigation water needs in Java is still in the surplus category, even though there are deficits in several catchment areas (WS): in the Kepulauan Seribu, Wiso Gelis, and Welang Rejoso WS. WS with the most water availability is generally located in wide (WS) areas, while several WS with abundant water needs is generally located in WS with the densest population. According to The Central Bureau of Statistics (BPS), the agricultural area in Java has decreased by an average of 20 thousand hectares per year, so that the demand for irrigation water on the island of Java will also decrease. Consequently, the excess water potential in Java Island needs to be allocated to meet the needs of DMI, which are increasing every year. In addition, the results also show that the development of irrigation areas in the future should be focused on large (WS) areas that have the potential for significant amounts of irrigation water.

An excessive groundwater usage is happening in Jakarta, Indonesia, due to the population growth and industrial development so that it experiences a significant groundwater drawdown which could enhance the risk of seawater intrusion and land subsidence. Existing conditions in 2018 show that seawater intrusion occurred at the Western and Central coastal area and land subsidence happen in the Northern and Central part. This research, a numerical simulation, is conducted by modeling such causality during the critical period, the next 20 years. The result shows that for every groundwater drawdown of 10 m/year, it will cause intrusion 0.7 km/year in the Western and Central and 1.1 km/year in the Eastern area after 2028. The 10 m/year groundwater drawdown also results in land subsidence of 5.7 cm/year in the Northern and 2.5 cm/year in Central Jakarta. This result is useful as an input for groundwater management policies and to prevent the environmental impacts occurred at other large coastal cities.

Increasing demand for water requires the improvement of water infrastructure. Dams are one of the most prominent infrastructures for water supply, especially as water demand increases. Due to its size, the dam is bound to affect the local environment, including the hydrometeorological and hydro/geological condition. The impact of dam on the local scale is supposedly dependent on several variables, namely, the height of the dam, its age, and the area of the river basin. This study studies the impact of dams on the surrounding environment by investigating 12 dams located in Java and are spread all throughout Java in particularly West Java, East Java, Central Java and lastly Jogjakarta. The dam environmental impact will be analyzed using: firstly, linear regression to determine the relationship between dams and environmental impact and secondly cluster analysis to divide the researched dams into categories. Dams in the study area could be divided into three clusters based on the similarity in height, age and river basin area. Additionally, this study finds that there is no correlation between the river basin area and both (ground) water quality and local climate. However, there was a correlation between the dam height with temperature and precipitation, as well as the dam age with Dissolved Oxygen (DO), Total Dissolved Solid (TDS) and pH. Regarding groundwater, the values of DO, TDS and pH are higher in dams located inside of groundwater basins compared to the opposite.