| The Huang-Huai-Hai plain (3H plain) is recognized as an important grain production area innorthern China, and where winter wheat-summer maize rotation is the main cropping systems.Currently,3H plain has become one of the most prominent contradiction areas between water supplyand demand due to over-exploited water resources, uneven spatial-temporal distribution of precipitation,and mismatch between precipitation and crop water requirements. How to develop the agricultural wateruse efficiency, reduce agricultural water use and improve crop water productivity has become a keyissue to resolve contradictions between agricultural water and continued high yield in3H plain. As theprimary data source, MODIS remote sensing, statistics, meteorological data, crop growth period dataand ground survey data in2001-2002,2006-2007, and2011-2012were used in crop informationextraction, crop yields rasterizing, actual evapotranspiration estimation and crop water productivity(CWP) calculation. Spatial and temporal variation of crop water productivity was investigated in orderto reveal the key factors of crop water productivity. In addition, the way to improve crop waterproductivity was discussed in3H plain. The results is expected to provide a basis information foragricultural water management, improvement of crop water productivity and choice of adaptivemechanism under climate change in3H plain. The main results are as follows:(1) The water consumption by actual evapotranspiration is estimated with Surface Energy BalanceAlgorithm for Land (SEBAL) model taking meteorological data and MODIS products as input. Theaverage instantaneous net radiation flux, soil heat flux, sensible heat flux and latent heat flux of3Hplain were558.92W·m-2,56.97W·m-2,56.97W·m-2and282.22W·m-2respectively in97(April7th)2011. Average daily evapotranspiration of3H plain was4.39mm and4.87mm in winter wheat andsummer maize rotation, after extracted by the crop dominant map. Results showed that SEBAL issuitable for estimating evapotranspiration in winter wheat and summer maize rotation in3H plain, basedon the comparation between evapotranspiration measured by Yucheng (in Shandong province) andevapotranspiration estimated by SEBAL. Actual evapotranspiration of winter wheat and summer maizewere calculated by space interpolation method, and spatial distribution of actual evapotranspiration inwinter wheat and summer maize growing season were mapped. Actual evapotranspiration in winterwheat growing season was found higher than that in summer maize growing season. Average value ofevapotranspiration in summer maize growing season were448.87mm,440.39mm and354.83mmrespectively in2001to2002,2006to2007and2011to2012, while630.70mm,550.76mm and538.41mm in winter wheat growing season. Crop evapotranspiration showed a decreasing tendency inthese three periods. Crop evapotranspiration was found more relative to NDVI in mid and late growingstages. Compared to NDVI, significant negative correlation was detected between evapotranspirationand surface temperature. Evapotranspiration in summer maize growing season showed significantcorrelation with longitude, which increase1degree will lead an reduce of13.71mm in summer maizeevapotranspiration. There is a significant correlation between evapotranspiration of winter wheat and latitude. Latitude, for each additional1degree, evapotranspiration of summer maize will reduce19.93mm.(2) The statistical cropped area and production data were synthesized to calculate district-level landproductivity, which is then further extrapolated to pixel-level values with1km×1km using MODISNDVI product based on crop dominance map. An increasing tendency was detected in crop productivityin3H plain. Yield of summer maize in2001was approximately350to450kg/mu with the average valueof383.4kg/mu and with higher value detected in Shijiazhuang-Jinan line, as well as the southern partof Jiangsu province. Yield of summer maize was400to500kg/mu in2006, and high yield area waslocated in Hebei, Henan and Shandong provices. Summer maize yield has increased to more than400kg/mu in2011, with high yield area located in Hebei, Shandong and Jiangsu provinces. Yield ofwinter wheat yield was250to400kg/mu in2002with the average value of332.0kg/mu, and high yieldarea was located in southern Hebei, northern Henan and Shandong provices. Winter wheat yield hasincreased to350to450kg/mu area in2007, with high yield area located in Hebei, Henan and Shandongprovinces. Yield of winter wheat yield in2012can reach to400kg/mu in most part of3H plain, withhigher value detected in Shandong and Henan provinces.(3) WP maps are then generated by dividing the rice productivity map with the actualevapotranspiration (ETa) maps. WP of summer maize (MWP) in most part of3H plain was less than1.4kg·m-3in2001, with regional average value1.37kg·m-3. High MWP area was found located inShandong province. MWP in most part of3H plain has increased to more than1.4kg·m-3in2006, withhigher MWP area located in Shandong province. Average MWP has increased to1.93kg·m-3in2011,and high-value WP area was located in Shandong and Jiangsu Provinces. MWP showed animprovement in Beijing and Tianjin, Hebei, Henan and southwestern region of Shandong during thesethree periods, while in eastern part of Shandong and Jiangsu province, MWP was detected with avolatility increase trend. WP of winter wheat (WWP) was less than0.9kg·m-3in2002, with regionalaverage value of0.81kg·m-3. High-value WP area was located in east part of Shandong and mid part ofHebei. WWP increased to1.09kg·m-3in2007, and detected with higher value in Shandong, Henan andHebei provinces. The regional average value is1.21kg·m-3in2012. In addition, WWP showed a greatvolatility except Anhui, entral and northern part of Hebei and parts of Shandong, where WWP improvedslowly and steady.(4) Significantly positive correlation and negative correlation were detected between CWP andP-ETa (precipitation deficit) and ETa-Etc (crop water demand deficit) respectively over3H plain. Thewestern part was identified as potential area for MWP, while central and southern areas for WWP. Twomeasures should be strengthened to improve crop water productivity in inference to the actual situationof farmland water budget of3H plain followed by reducing ETa through regulating crop transpirationluxury and soil surface evaporation and then cutting down the unreasonable use of water resourcesthrough optimization of irrigation system. Crop yield and water consumption are acknowledged as a complex process due to crop varieties,human management and so on together with meteorological variables. The non-climatic factors andinfluence mechanism is expected to investigate based on crop model with the purpose of improvingcrop water productivity. |
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