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Abstract:The spatial and temporal variability of precipitation time series were investigated for the Hexi Corridor, in Northwest China, by analyzing the entropy information. The examinations were performed on monthly, seasonal, and annual timescales based on 29 meteorological stations for the period of 1961-2015. The apportionment entropy and intensity entropy were used to analyze the regional precipitation characteristics, including the intra-annual and decadal distribution of monthly and annual precipitation amounts, as well as the number of precipitation days within a year and a decade. The regions with high precipitation variability are found in the western part of the Hexi corridor and with less precipitation, and may have a high possibility of drought occurrence. The variability of the number of precipitation days decreased from the west to the east of the corridor. Higher variability, in terms of both of precipitation amount and intensity during crop-growing season, has been found in the recent decade. In addition, the correlation between entropy-based precipitation variability and the crop yield is also compared, and the crop yield in historical periods is found to be correlated with the precipitation intensity disorder index in the middle reaches of the Hexi corridor.

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<p>The increase in atmospheric carbon dioxide (CO<sub>2</sub>) concentration is changing plant physiology, thus affecting terrestrial hydrological response. A nonlinear stomatal conductance response to carbon dioxide concentration (gs – CO<sub>2</sub>) was incorporated in the VIC model for better representation of the evapotranspiration (ET) response to the elevated CO<sub>2</sub>. The annual ET of maize and wheat over the agricultural land in Northwest China was found to decrease by 0.54% and 0.21% during 1980–2010, respectively. Under doubled CO<sub>2 </sub>concentration (660 ppm), the ET reduction of maize and wheat was 23.3 mm and 8.9 mm, which accounted for 4.3% and 1.8% of the corresponding annual ET. The annual ET reduction of maize, under the four future scenarios (RCP4.5_2040s, RCP4.5_2080s, RCP8.5_2040s, and RCP8.5_2080s), was about 1.1–6.4%, resulted from an ensemble mean of eight general circulation models. The effects of elevated CO<sub>2 </sub>offset part of ET increase caused by the precipitation and temperature changes. This study has practical implications for precise irrigation. The ET response of maize should be paid more attention for its larger potential in saving irrigation water for the studied region. The elevated CO<sub>2 </sub>concentration will be beneficial for saving irrigation water to a certain degree.</p>