Annual assessment of Kashafrood watershed basin climate components in future periods by using fifth report of intergovernmental panel on climate change

Hydrology cycle of river basins and water resources availability in arid and semi-arid regions are highly affected with climate changes. So that in the recent years, increase of temperature due to increase of greenhouse gases have led to anomaly in the Earth’ climate system. At present, General Circulation Models (GCMs) are the most frequently used models for projection of different climatic change scenarios. Up to now IPCC has released 4 different versions of GCM models including: First Assessment Report models (FAR) in 1990, Second Assessment Report models (SAR) in 1996, Third Assessment Report models (TAR) in 2001 and Fourth Assessment Report models (AR4) in 2007. The purpose of this study is to survey the annual trend of the future climate components in kashafrood watershed basin (located in the northeastern part of Iran and in the khorsan razavi province) by using fifth report of Intergovernmental panel on climate change (IPCC) under new emission scenarios.
Material and In this research, keeping in view the importance of precipitation and temperature parameters, fourteen models obtained from the General Circulation Models (GCMs) of the newest generation in the Coupled Model Intercomparison Project Phase 5 (CMIP5) were used to forecast the future climate changes in the study area. In historical time (1992-2005), simulated data of these models were compared with observed data using four evaluation criteria for goodness-of-fit including Nash-Sutcliffe (NS), Percent of Bias (PBIAS), coefficient of determination (R2) and the ratio of the root mean square error to the standard deviation of measured data (RSR).
According to performance criteria, among 14 models used in this research, four was chosen as the best namely GFDL-ESM2G, IPSL-CM5A-MR, MIROC-ESM and NorESM1-M which indicated more agreement with observed data. Furthermore, four Representative Concentration Pathways (RCPs) of new emission scenario, namely RCP2.6, RCP4.5, RCP6.0 and RCP8.5 under three future periods: near-century (2006-2037), mid-century (2037-2070) and late-century (2070-2100) were investigated and compered.
The results of Mann-Kendall (MK) test which was applied to examine annual trend, revealed that the precipitation have a variable positive and negative trends which were statistically significant. Also mean, maximum and minimum temperature have a significant positive trend with 90, 99 and 99.9% confidence level. On the other hand, in all parts of the Kashafrood Watershed Basin (KWB), average temperature of watershed increased up to 0.56 °C - 3.3 °C and precipitation decreased up to 10.7% until the end of the 21st century in relation with the historical baseline.