ASSESSMENT OF CLIMATE CHANGE AND ITS IMPACTS IN RIVER BASIN PLANNING

Abstract

River basin has been viewed as the ideal unit to address water resource issues comprehensively. Water resources and hydrological dynamics in river basin are altered by changes in climate and land cover. The effect of climate change on river basin, connected with hydrological systems varies regionally and between climate scenarios. To assess the hydrological effects of environmental change, several methods were developed, which mainly fall into two groups, time series analysis (statistical method) and hydrological modeling. The statistical methods were used to examine temporal trends and their spatial distribution of historical annual and seasonal precipitation and temperature series in the past of two decades. Non-parametric tests, Mann—Kendall (MK) method searches for detecting and assessing significant trend in hydro-climatic time series, without specifying whether the trend is linear or nonlinear. The true slope (change per unit time) was estimated by using a simple non-parametric procedure developed by Sen method. Hydrological modeling, especially distributed hydrological modeling, is used to simulate hydrological processes in watersheds. Soil and Water Assessment Tool (SWAT) is applied to estimate and understand to the hydrology behaviour of Upper Brantas basin. SWAT model was calibrated and validated using the observed discharge data. Monthly discharge of 1998-2002 and land cover map 2003 were used for model calibration and validation. The sensitive parameter to improve the calibration efficiency is necessary. Coefficient of determination (R2), Nash-Sutcliffe index (NSE), Percentage Bias (PBIAS), and Ratio of the Root Mean Square Error to the standard deviation of measured data (RSR) were used to evaluate the model in order to get goodness of fit. Land cover/climate change is predicted to have important impacts on river flows and water resources. The effect of land cover only on the model response were assessed by running the calibrated model and keeping the DEM, soil maps and climatic data constant while changing only the land" cover. On the other side, the impacts of land cover/climate change were estimated by defining combination scenarios for climatic inputs and land cover Im maps to a hydrological model. Two different periods (1984-1995 and 1996-2006) of climatic data and land cover map for 1989 and 2001 were used to present land cover condition of the two periods. Considering information from IPCC for the twentieth century (2020s) and also from the trend analysis result, changes in temperature were set at T -1°C up to +1°C and those for rainfall were set to P -5% up to P+5% for the different climatic sensitivity scenario. These values were adopted because sometimes extreme events have increased in frequency in recent years and are likely to continue to increase in the future. The prediction future climate conditions were determined using the Special Report of Emission Scenario (SRES) by IPCC. Response of hydrological processes to the land cover change, land cover/climate changes and sensitivity scenario had made variation in the water volume in the Upper Brantas river basin. Somehow it gives good or bad effects to the basin environment system. Therefore this result of this study together with an integrated basin management is required to make a good decision making process in order to get the best environment condition to adapt meteorological phenomena in this river basin.