Temporal changes in seasonal precipitation over the Sahara Desert from 1979 to 2016

Rainfall variability dominates livelihoods in all countries of Saharan Africa. To better understand the processes involved in Sahara precipitation changes, we used the Global Precipitation Climatology Center(GPCC) dataset to examine dry and wet seasonal trends in the Sahara region from 1979 to 2016. We also used the European Centre for Medium-Range Weather Forecasts(ECMWF) to evaluate the general atmospheric circulation associated with seasonal change of Sahara precipitation. The Mann-Kendall test and Theil sens' slope estimator methods were adopted to test and estimate the significance and weight of precipitation trend, respectively. The results revealed that Sahara precipitation has increased significantly.The seasonal evaluation shows a positive trend of 0.42 mm/decade and 1.43 mm/decade in JAS(June, August, and September) seasons for the northern and southern Saharan Desert, respectively. Moreover, the JFMA(January, February,March, and April) period shows a negative trend but not statistically significant. An examination of the general circulation and moisture transport changes suggested an increase of rainfall in southern Sahara. The wet period is also driven by northward penetration of moisture originating from the Sahel region, African Easterly Jet(AEJ), and weakening in the upper tropospheric zonal wind. Summer rainfall has also been likely associated with positive anomalies of sea surface temperature(SST) in the North Tropical Atlantic(NTA) and the Mediterranean Sea.     

Application of geodetector in sensitivity analysis of reference crop evapotranspiration spatial changes in Northwest China

Reference crop evapotranspiration (ET_0) is an important parameter in the research of farmland irrigation management,crop water demand estimation and water balance in scarce data areas,therefore,it is very important to study the factors af‐fecting the spatial variation of ET_0.In this paper,the Penman-Monteith formula was used to calculate ET_0which is the de‐pendent variable of elevation (Elev),daily maximum temperature (T_(max)),daily minimum temperature (T_(min)),daily average temperature (T_(mean)),wind speed (U_2),sunshine duration (SD) and relative humidity (RH).The sensitivity analysis of ET_0was performed using a Geodetector method based on spatial stratified heterogeneity.The applicability of Geodetector in sensitivity analysis of ET_0was verified by comparing it with existing research results.Results show that RH,T_(max),SD,and T_(mean)are the main factors affecting ET_0in Northwest China,and RH has the best explanatory power for the spatial distribu‐tion of ET_0.Geodetector has a unique advantage in sensitivity analysis,because it can analyze the synergistic effect of two factors on the change of ET_0.The interactive detector of Geodetector revealed that the synergistic effect of RH and T_(mean)on ET_0is very significant,and can explain 89%of the spatial variation of ET_0.This research provides a new method for sensitivity analysis of ET_0changes.