Propagation characteristics from meteorological drought to agricultural drought over the Heihe River Basin, Northwest China

In the context of global warming,drought events occur frequently.In order to better understanding the process and mechanism of drought occurrence and evolution,scholars have dedicated much attention on drought propagation,mainly focusing on drought propagation time and propagation probability.However,there are relatively few studies on the sensitivities of drought propagation to seasons and drought levels.Therefore,we took the Heihe River Basin(HRB)of Northwest China as the case study area to quantify the propagation time and propagation probability from meteorological drought to agricultural drought during the period of 1981–2020,and subsequently explore their sensitivities to seasons(irrigation and non-irrigation seasons)and drought levels.The correlation coefficient method and Copula-based interval conditional probability model were employed to determine the drought propagation time and propagation probability.The results determined the average drought propagation time as 8 months in the whole basin,which was reduced by 2 months(i.e.,6 months)on average during the irrigation season and prolonged by 2 months(i.e.,10 months)during the non-irrigation season.Propagation probability was sensitive to both seasons and drought levels,and the sensitivities had noticeable spatial differences in the whole basin.The propagation probability of agricultural drought at different levels generally increased with the meteorological drought levels for the upstream,midstream,and southern downstream regions of the HRB.Lesser agricultural droughts were more likely to be triggered during the irrigation season,while severer agricultural droughts were occurred mostly during the non-irrigation season.The research results are helpful to understand the characteristics of drought propagation and provide a scientific basis for the prevention and control of droughts.This study is of great significance for the rational planning of local water resources and maintaining good ecological environment in the HRB.

Tropical Stratospheric Circulation and Monsoon Rainfall

Interannual variability of both SW monsoon (June-September) and NE monsoon (October-December) rainfall over subdivisions of Coastal Andhra Pradesh, Rayalaseema and Tamil Nadu have been examined in relation to monthly zonal wind anomaly for 10 hPa, 30 hPa and 50 hPa at Balboa (9°N, 80°W) for the 29 year period (1958-1986). Correlations of zonal wind anomalies to SW monsoon rainfall (r = 0.57, significant at 1% level) is highest with the longer lead time (August of the previous year) at 10 hPa level suggesting some predictive value for Coastal Andhra Pradesh. The probabilities estimated from the contingency table reveal non-occurrence of flood during easterly wind anomalies and near non-occurrence of drought during westerly anomalies for August of the previous year at 10 hPa which provides information for forecasting of performance of SW monsoon over Coastal Andhra Pradesh. However, NE monsoon has a weak relationship with zonal wind anomalies of 10 hPa, 30 hPa and 50 hPa for Coastal Andhra Pradesh, Rayalaseema and Tamil Nadu.Tracks of the SW monsoon storms and depressions in association with the stratospheric wind were also examined to couple with the fluctuations in SW monsoon rainfall. It is noted that easterly / westerly wind at 10 hPa, in some manner, suppresses / enhances monsoon storms and depressions activity affecting their tracks.

蒙古高原植被净初级生产力干旱风险

The increasing frequency of recent droughts has an adverse effect on the ecosystem of the Mongolian Plateau.The growth condition of NPP is considered an indicator of the ecological function.Therefore,identifying the relationship between NPP and drought can assist in the prevention of drought-associated disasters and the conservation of the ecological environment of the Mongolian Plateau.This study used the Carnegie-Ames-Stanford Approach(CASA)model to simulate the NPP capacity of the Mongolian Plateau between 1982 and 2015,as well as drought indicators(drought probability,vulnerability,and risk)to explore the drought risk of NPP.The findings pointed to an overall increase in NPP with regional variances;however,the NPP rate in Inner Mongolia was considerably higher than that in Mongolia.The standardized precipitation evapotranspiration index(SPEI)showed an overall downward trend,with Inner Mongolia experiencing a substantially lower rate of decline than Mongolia.The areas most likely to experience drought were primarily in the center and north while the areas with the highest drought vulnerability were primarily in the northeast,center,and southeast.Mongolia showed a higher probability of drought compared to Inner Mongolia.Drought-prone regions of the Mongolian Plateau increased during the 21st century while drought-vulnerable areas increased and shifted from north to south.Alpine grasslands and coniferous forests were least vulnerable to drought,while other vegetation types experienced temporal variation.In the 21st century,the primary determinants of drought risk shifted from precipitation and the normalized difference vegetation index(NDVI)to temperature and relative humidity.