The Agricultural Drought and Flood Index and Its Operational Application to Monitoring and Early-warning in Jianghuai Area

An accumulated humidity index is introduced as agricultural drought and flood indicator and can be applied to operation. The index bases on the relative humidity index, replacing evapotranspiration with the crop water requirements, and the influence of former drought and flood status to current ones is considered too. Each component's time efficiency and effect weight varies on different temperature condition.The effect weight of every ten days are also different.The reference evapotranspiration is estimated and calibrated using temperature data of actual measurement, and errors are eliminated to meet application requirement, thus FAO Penman-Monteith is available for operation. The macroscopical crop water requirements is obtained by compositive crop coefficients in different region, also the grades of drought and flood index of a ten-day period in the humid and semi-humid zones are established.Used in agricultural drought and flood monitoring, and the qualitative coincident between this index and the soil moisture indices reaches 80%—90%, and quantitative coincident percentage is 60%—70%. The soil moisture data of longer serial stations are more consistent with accumulated humidity index than with regional survey result; normal and relative normal drought and flood grade leads to the highest coincident rate, drought the second, while flood leads to a relative low result. Since there is great difference between the soil moisture and cumulated humidity index in the monitoring aging and means, 10%—20% errors can be considered acceptable. Considering the index of the coincident ratio for stations, every grade samples proportion of total and its coincident ratio, the accumulated humidity index reflects soil moisture status in general.This index is used in agricultural drought and flood early-warning, the reliability of which is influenced by medium-term forecast.It contains former droughts and flood facts, making the trend relatively accurate on the whole. Considering the operation requirement, the early-warning precision still needs improvement. On one hand, the day-to-day data can be obtained by analyzing information of middle-term precipitation course prediction; on the other hand, statistical method is used to predict the index on basis of temporal characteristics analysis, to adjust the error of precipitation prediction, and improve the accuracy of agricultural drought and flood early-warning.The agricultural drought and flood are primary agrometeorological disasters in China, so the monitoring and the early-warning operation is a key agrometeorological job. At present, there are indexes on agricultural drought and flood such as soil moisture index, remote sensing index and meteorological index. But considering the complexity of agricultural drought and flood, the above indexes each has advantage and weakness, therefore strengthening research on compositive technique for the agricultural drought and flood is necessary.