Cumulative ecohydrological response to hydrological processes in arid basins

Abstract

Abstract As a main anthropogenic hydrological process in arid areas, an ecological water conveyance project usually shows profound effects on the hydro- and bio-systems in the region. In order to explore novel methods and theories to assess cumulative effects of human activities on an ecological system, this study presents a method of cumulative ecohydrological response curves to quantitatively evaluate the effects of an ecological water conveyance project which the lag time of the cumulative response and growth rates of the cumulative effects can also be identified. With the lower Tarim River, Northwest China as a case study, we analyzed the spatiotemporal variations of the cumulative ecohydrological response in terms of two indicators, groundwater depth and vegetation coverage, based on the eighteen phases of the ecological water conveyance project. The cumulative ecohydrological response to the ecological water conveyance project was evaluated with an integrated methodology of combining the Spearman empirical statistical model, the dimidiate pixel model and the Kriging Interpolation. A cumulative ecological water conveyance volume model was further built using the Four-Parameter Logistic Model to make the cumulative response quantifiable. The cumulative quantified scheme can give a keen insight into the cumulative effects of hydrological processes under the influence of human activities. The cumulative ecohydrological response shows that: 1) the cumulative effects reflected by the positive correlation among the cumulative ecological water conveyance volume, the groundwater depth and the vegetation coverage, 2) there existed time lags in the cumulative time response, 80-day lag for groundwater and 4–7 years lag for vegetation, 3) and the cumulative spatial response of groundwater depth and vegetation was deduced. Our results suggest that the ecological water conveyance volume can be lowered to 0.5 × 108–1.5 × 108 m3 at each period. With a reasonable water conveyance strategy, the cumulative effects can reach the groundwater depth at 3.6885 m–3.7651 m and the vegetation coverage at 0.1339–0.1374 after the 5 phases of water infusion in consecutive years.