Climate change is a global phenomenon that become a concern. Climate change affects the hydrological conditions of a watershed, including rainfall. Saguling Reservoir has a high erosion rate on the watershed. One factor that affects erosion based on USLE is the rain erosivity index which has a relation with rainfall amount. So the climate change effect of rainfall on erosivity factor in Saguling Reservoir watershed needs to be investigated because it will affect the erosion rate which is useful to determine the sedimentation rate of the reservoir. The purpose of this study was to analyze the effect of climate change on the erosivity index. Climate change (rainfall) was analyzed using GCM CanESM2 Model in the RCP scenario through a downscaling process. Downscaling has been done with SDSM. The rain erosivity index was analyzed using Lenvain’s formula. Downscaling with the SDSM method was able to give good results based on the coefficient of determination and it was found that there was a change of monthly rainfall in the short, medium, and long term periods, as well as an increase in annual rainfall up to 34.3%. The annual rainfall erosivity index changes along with changes in rainfall due to climate change and there is an increase of up to 44.1%. ABSTRAK Perubahan iklim merupakan fenomena global yang kini menjadi perhatian. Perubahan iklim mempengaruhi kondisi hidrologi suatu DTA (Daerah Tangkapan Air) antara lain terjadinya perubahan curah hujan. Waduk Saguling memiliki laju erosi tinggi pada DTA. Salah satu faktor yang mempengaruhi erosi berdasarkan Persamaan USLE adalah indeks erosivitas hujan yang terkait erat dengan besarnya curah hujan. Sehingga Pengaruh perubahan iklim terhadap faktor erosivitas hujan di DTA Waduk Saguling perlu diteliti karena akan mempengaruhi laju erosi yang berguna untuk menentukan laju sedimentasi waduk. Tujuan penelitian ini adalah menganalisis pengaruh perubahan iklim terhadap indeks erosivitas hujan. Analisis perubahan iklim (curah hujan) dilakukan dengan Model GCM CanESM2 skenario RCP melalui proses downscaling. Downscaling dilakukan dengan metode SDSM. Indeks erosivitas hujan dianalisis berdasarkan rumus Lenvain. Downscaling dengan metode SDSM mampu memberikan hasil yang baik berdasarkan koefisien determinasi dan didapatkan perubahan curah hujan bulanan pada periode jangka pendek, menengah dan panjang, serta untuk curah hujan tahunan terdapat peningkatan hingga 34,3%. Indeks erosivitas hujan tahunan di DTA Waduk Saguling mengalami perubahan seiring dengan berubahnya curah hujan akibat perubahan iklim dan terdapat peningkatan hingga 44,1%.

Bula District is strategic region in Seram Bagian Timur Regency which often experienced flood event especially in downstream areas. Flood Event that occurs causing loss of materials, even human life. This research was conducted to identify inundation that caused by the flood using two-dimensional inundation model. Model’s component consists of three part those are hydrology module, flood routing and inland flooding. Flood simulation result was calibrated with flood observation map in Bula District. Flood simulation resulted with flood discharge 25-year times period shows that inundation area that probably happen in Bula District is 5,4 km2 and flood volume that probably happen is 7,406,708 m3. Bila Besar Watershed contribute >70% to flood event that occurs based on inundation area and flood volume. Based on map overlay between simulation result into Satellite Google Imagery shows that 31.8% of 2,390 unit building in Bula District probably inundated by flood.