Drought Variation and Its Sensitivity Coefficients to Climatic Factors in the Yellow River Basin

Investigation of the variation in drought and regional response to climate change is widely accepted to be very important for ecological security and agricultural production, and can provide basis information for developing appropriate measures to reduce droughts over the Yellow River Basin (YRB). In this study, the relative humidity index (M) was calculated from a data set of daily climate variables in 102 meteorological stations over the Yellow River Basin and in sequence, its sensitivity coefficients to key meteorological variables were firstly investigated using a partial derivative method. The results witnessed that the drought degree was detected to be stronger in the upper region than the middle and lower region. Moderate, slight, moderate and extra severe drought were found in spring, summer, autumn and winter respectively and extra severe drought was found in entire year. M was detected to increase from the northwest to the southeast region and the extra severe drought region was mainly located in Shaanxi, Shanxi, north Ningxia and Inner Mongolia. The meteorological stations whose relative humidity index increased were mainly located in the upper region, while in the southeast region of YRB. Accordingly, the M is proved to be positively sensitive to solar radiation (RS) and relative humidity (RH), while negatively sensitive to air temperature (T) and wind speed (WS). The M was most sensitive to RS and T for summer in upper and middle region respectively. Furthermore, the most sensitive variable turned to be RH for spring, autumn, winter and entire year in the whole basin. The declining of RH controlled a negative trend for M in spring and summer over the whole basin, while RS was primarily responsible for the change of M in autumn in upper and lower region respectively. However, the primarily controlling variable turned to be T, WS and WS for winter in upper, middle and lower region. As for the entire year, RS, RH and RH mainly governed M in upper, middle and lower basin respectively.