日尺度标准化前期降水蒸散指数及其在安徽省的适用性分析

旱涝灾害是影响农业丰产增效的主要灾害之一。目前广泛应用的旱涝指数，多以旬、月、季尺度的旱涝指数为主，其时效性与精准性水平与农业旱涝灾害绿色应对和防控服务需求还有差距。本文选取位于南北气候过渡带的安徽省，应用78个地面气象观测站数据，通过对日尺度前期降水蒸散差值指数（antecedent precipitation evapotranspiration index，APEI）序列值进行三参数log-Logistic概率分布拟合，构建日尺度的标准化前期降水蒸散指数（standardized antecedent precipitation evapotranspiration index，SAPEI），并在沿淮淮北、江淮之间、沿江江南不同干湿性区域选取代表站，对SAPEI在安徽省旱涝监测评估中的适用性进行分析。结果显示：不同区域代表站APEI序列的经验概率分布曲线与log-Logistic理论概率分布曲线高度拟合，有无降水时逐日SAPEI曲线能反映农田水分收支状况；2011年6月8日、6月28日旱涝急转应用案例中，SAPEI旱涝等级与变化趋势，与同期土壤水分监测的旱涝等级与演变趋势具有很好一致性。基于SAPEI的小麦全生育期累年平均旱涝积空间分布，符合安徽省实际旱涝分布型；全生育期SAPEI累年平均值（I_SAPEI）的0值线以北、以西为负值、偏干区域，与安徽省小麦主产区一致。研究表明，日尺度的SAPEI及其旱涝积指数，可以反映降水时间分布及日雨量大小对旱涝的影响，精准刻画安徽省不同区域日尺度的旱涝变化及旱涝过程累积效应，可在安徽省旱涝逐日动态监测与农业旱涝影响评估服务中应用。

Daily standardized antecedent precipitation evapotranspiration index (SAPEI) and its adaptability in Anhui Province

Agricultural drought and waterlogging are two of the most compelling problems affecting agricultural productivity and efficiency. At present, most of the widely used drought and waterlogging indices are based on ten-day, monthly, and seasonal scales. Their timeliness and accuracy are still far from the desired levels that would enable a sustainable means of preventing and controlling agricultural drought and waterlogging disasters. Based on the data of 78 meteorological observing stations in Anhui Province, selected as the transitional zone between the North Semi-humid and South Humid climates, a daily standardized antecedent precipitation evapotranspiration index (SAPEI) was constructed by fitting the daily antecedent precipitation evapotranspiration index (APEI) series with a 3-parameter log-logistic distribution. In addition, its feasibility and adaptability were analyzed in representative stations that were selected in different dry and wet zones, namely, North of the Huaihe River, Between the Huaihe River and Yangtze River, and South of the Yangtze River. The results showed that the empirical probability distribution curve of representative stations'' APEI series highly corresponded with the theoretical log-logistic distribution curve. Representative stations'' daily SAPEI curve could describe the changes in farmland water budget in the presence/absence of rain. In the case of the rapid change in drought and flood on June 8 and 28, 2011, SAPEI''s drought and waterlogging grade and change trends were in good agreement with soil moisture in the same period. Spatial distribution of drought, waterlogging frequency, and annual mean values of accumulated index based on winter wheat whole development stage''s SAPEI was primarily distributed latitudinally. These distribution characteristics conformed to the actual distribution of drought and waterlogging in Anhui Province. The 0-value line of annual mean SAPEI (I_SAPEI) in the winter wheat whole development stage was located north of the "Between the Huaihe River and Yangtze River" zone and along the eastern and southern foot of the Dabie Mountains. The area covered by negative values was drier and was the main area planted with winter wheat in Anhui Province, and the other area covered by positive values was more humid. In conclusion, the daily-scale SAPEI and its accumulated index could reflect the temporal distribution of precipitation and the impact of daily rainfall amount, and accurately depict the changes in drought and waterlogging and the cumulative effects of drought and waterlogging processes in different regions of Anhui Province. Therefore, SAPEI not only retained the advantages of standardized precipitation evapotranspiration index (SPEI) such as strong regional applicability, dimensionless character, and the ability to reflect the influence of temperature, but also had higher timeliness and sensitivity by modifying the precipitation evapotranspiration index from a monthly or seasonal scale to a weighted cumulative precipitation evapotranspiration index at a daily scale. SAPEI can be used in daily dynamic monitoring and the assessment process of drought and waterlogging in Anhui Province.