Evaluating climate and irrigation effects on spatiotemporal variabilities of regional groundwater in an arid area...

Groundwater level is an important variable in the evolution process of ecological environment systems. However, spatiotemporal changes in groundwater level are attributed to the comprehensive influence of natural and anthropogenic activities. Therefore, understanding the major driving forces to changes in spatiotemporal patterns of groundwater level is essential for sustainable utilization of regional groundwater and sustaining healthy ecosystems, especially in arid areas. In this study, based on monthly observations of depth to groundwater table (DTGT) from 67 monitoring wells during 2001-2010 in the Yichang Irrigation Sub-district (YISD) of the Hetao Irrigation District (HID), which is located in Northwest China with an arid climate, the empirical orthogonal function (EOF) method was used to analyze the spatiotemporal variations of DTGT and the major driving forces. The EOF analysis results showed that the first two spatial structures (EOF1 and EOF2) of DTGT were found in this region, which explained over 65% and 8% of the spatial variation of DTGT, respectively. Meteorological factors (evaporation and temperature) were the first leading factors to drive the temporal pattern of the first expansion coefficient (EC1) corresponding to the EOF1 at intra-annual scale as well as inter-annual scale. Particularly, temperature controlled the EC1 pattern during the freezing period from December to March. Soil texture was shown to have good correlations with the spatial patterns of DTGT, although these correlations diminished when the depth exceeded 250 cm. This study provides strong evidence that the principal spatiotemporal variations of groundwater can be effectively extracted by the EOF method, thereby obtaining integrated views of the relationships between the groundwater system and meteorological and anthropogenic factors.