Study On Evapotranspiration Of Vegetation In Water-Wind Erosion Crisscross Region On The Loess Plateau

The water-wind erosion crisscross on the Loess Plateau is a special region. The distribution of precipitation is unbalance and evapotranspiration is higher so deficit of water becomes a key problem to sustainable development of the agriculture in this area. Therefore it is important to use limited water resources and choose feasible vegetation to improve ecological and social environment. In this dissertation, a large weighing lysimeter, micro weighing lysimeter and evaporation pan are used in this experiment to study evapotranspiration of the four plants and establish KC and KP equations. Meantime weather generator is also tested on the Loess Plateau. The main results obtained from this study are as follows:(1) Change of vegetations height and coverage complies with"S"curve during the different growing stages. The order of water consumption is as follow: Artemisia capillaris Thunb> Korshinsk Peashrub > alfalfa > Millet. The evapotranspiration were 254.8mm, 316.9mm, 343.4mm and 361.9mm for Millet, alfalfa, Korshinsk Peashrub and Artemisia capillaris Thunb respectively.(2) The effect of different environment to evaporation of the pan is different. The order of pan of evaporation is as follow: Bare land> Korshinsk Peashrub land> millet land> alfalfa land> Artemisia capillaris Thunb land. The pan evaporation of no plant was 976.2mm, The pan evaporation of Korshinsk Peashrub was 948.5mm, The pan evaporation of millet was 898.7mm, The pan evaporation of alfalfa was 941.8mm, The pan evaporation of Artemisia capillaris Thunb was 866.6mm.(3) The air temperature, relative humidity, solar radiation and wind speed were analyzed. The relationships among the evaporation of the pan, relative humidity and solar radiation are higher than the relationship between the evaporation of the pan and others. The evaporation of the pan became higher as relative humidity decreased and wind speed increased. The Kp estimated by relative humidity, wind speed and solar radiation can be used to compute ET0 combined with observed data from 20cm pan. There is a satisfactory correlation between ET0 of 20cm pan and Penman-Monteith method.(4) Crop water demands for four different vegetations were measured using a weighing lysimeter located in water-wind erosion crisscross on the Loess Plateau. The results showed that the relationship between crop coefficients and days after seeding can be represented by a third-order polynomial equation. The estimated values of the basal crop coefficients for millet at four growth stages were 0.23, 0.43 and 0.24 for initial, mid and late season. The estimated values of the basal crop coefficients for Artemisia capillaris Thunb at four growth stages were 0.58, 0.67 and 0.62 for initial, mid and late season. The estimated values of the basal crop coefficients for alfalfa at three growth stages were 0.48 and 0.52 for initial and mid season. The estimated values of the basal crop coefficients for Korshinsk Peashrub at three growth stages were 0.45 and 0.57 for initial and mid season respectively.(5) Large weighing lysimeter and micro-lysimeter are used to determine the daily alteration processes of soil evaporation and transpiration of millet in its growth stages. Precipitation can satisfy the need of millet but in some key growth stages the precipitation was deficit. In the millet growth stages about 44% of the total field evapotranspiration is consumed by the soil evaporation under canopy. The relationship between E/ET and leaf area index are analyzed as well as the relationship between E/ET and soil moisture at 10cm depth. The results show that both the correlation coefficients are higher than 0.8.(6) This study was conducted to calibrate LARS-WG with 50 year daily precipitation, temperature,and solar radiation during data of six meteorological sites on the Loess Plateau of China. Meantime, we stimulated future climate conditions on the Loess Plateau. The results showed that annual and monthly distribution of daily maximum and minimum temperature and solar radiation can be simulated accurately. However, annual precipitation and its monthly distribution was little greater than observed values. The estimated ET0 by LARS-WG is well consistent with calculated ET0 from climate factors. Meantime we use LARS-WG and KC to estimate water consumption of millet and Artemisia capillaris Thunb from 1991 to 2010.