Sensitivity and resilience of ecosystems to climate variability in the semi-arid to hyper-arid areas of Northern China: a case study in the Heihe River Basin

Climate variability and climate extremes are important climatic determinants of plant growth, species distribution and net primary productivity. A comprehensively quantitative analysis of the sensitivity and resilience of ecosystems to climate variability is vital to identify which regions and species are most in danger in response to future climate change. Here, we proposed an empirical approach to assess the relative sensitivity and resilience of ecosystems to short-term climate variability in the Heihe River Basin (HRB) which is the second largest inland river basin in the northern China and contains ecosystems of semi-arid, arid and hyper-arid types. Based on the monthly time series of normalized difference vegetation index (NDVI), land surface temperatures (LST) and the ratio of actual evapotranspiration to potential evapotranspiration (AET/PET) derived from MODIS sensor from 2000 to 2013, we developed a multiple linear regressive and autoregressive model to determine the sensitivity of NDVI anomalies to climate variability indicated by monthly LST anomalies (temperature variability) and monthly AET/PET anomalies (water variability). We included 1 month time lag of NDVI anomalies in order to reflect ecosystem resilience. We found that the sensitivity and resilience to climate variability were different in the upper, middle and lower reaches of the HRB. Temperature variability dominantly controlled vegetation anomalies in the upper reach, but water variability was the dominant climatic factor in the middle and lower reaches. The different responses of semi-arid to hyper-arid ecosystems to climate variability depended much on the distinct climatic conditions and diverse vegetation types. Ecosystems in drier condition tended to show higher sensitivity to water variability, and ecosystems with colder climate were likely to be more sensitive to temperature variability. The most sensitive vegetation type to water variability and temperature variability in the HRB was crop and meadow, respectively. Grass had been proved to have the lowest resilience. Our research on the sensitivity and resilience of semi-arid to hyper-arid ecosystems is helpful for formulating and implementing adaptation and mitigation strategies in response to climate change.