一、前言元江热坝区为云南高原的低谷地,四周环山,谷地内地势低凹,地理位置非常特殊,最低海拔仅370米,属北热带气候类型。据1954—1985年气象资料,年均温23.8℃,极端最高温42.3℃;年均地表(0厘米)温27.5℃;≥10℃年均积温8703℃;年均降雨量783毫米,5—10月为雨季,占全年总降雨量的77%;年均蒸发量2734毫米,为平均降雨量的3.5倍;年均日照时数2240小时, I. Preface The Yuanjiang Dam Area is the lowland of the Yunnan Plateau. It is surrounded by mountains and valleys and has a low lying position in the valley. Its geographical location is very special with a minimum elevation of 370 meters and belongs to the northern tropical climate. According to the meteorological data from 1954 to 1985, the annual average temperature is 23.8 ℃ and the extreme maximum temperature is 42.3 ℃. The average annual surface (0 cm) temperature is 27.5 ℃. The average annual accumulated temperature of ≥10 ℃ is 8703 ℃. The average annual rainfall is 783 mm and 5-10 The month is the rainy season, accounting for 77% of the total rainfall in the year; the average annual evaporation is 2734 millimeters, 3.5 times the average rainfall; the average annual sunshine duration is 2240 hours,