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Cao W.,Anhui Meteorological Institute | Cao W.,Anhui Province Atmospheric Science and Satellite Remote Sensing Key Laboratory | Duan C.F.,Anhui Climate Center | Shen S.H.,Nanjing University of Information Science and Technology
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2015

In the context of global warming, the impact of climate change on water resources is becoming increasingly significant and is thus drawing more attention. As a main component of the hydrological cycle, potential evapotranspiration (ET0) represents the maximum possible evaporation and is the rate of evaporation that would occur under given meteorological conditions from a continuously saturated surface. ET0 is essential for scheduling of irrigation system running times, preparing input data for hydrological models used in water balance studies, and assessing the hydrological impacts of the changing climate. Therefore, the trends of the changes in ET0 and its dominant factors across different regions of the world have been studied by many researchers in recent decades. Despite the global warming, decreasing trends in ET0have been detected in several countries, including the United States, Russia, India, China, Australia, and New Zealand. Decreasing sunshine hours, declining wind speed, and increasing relative humidity have been considered to be the main causes of the decreasing ET0.Analysis of the linear trend of the time series is frequently used in climate change research. The linear trend can reflect the overall trend of climate change over a time period, but it cannot describe the undulating character of climate change over a long time period. Thus, the characteristics of interdecadal turning of climatic factors, including air temperature, precipitation, and solar radiation, have become a topic of concern for many researchers worldwide.Thorough exploration of the interdecadal turning of ET0 trends can lead to a better understanding of the evolution and abrupt changes of ET0 related to climate change. Based on the FAO56 Penman-Monteith equation, interdecadal breakpoints in ET0 trends were studied using Tom- and Miranda’s climate-trend turning discriminatory model for 580 meteorological stations across China during 1971—2010. Differences in the trends and determining factors between the before and after breakpoint periods were also analyzed. The results showed that annual average ET0 decreased significantly (-2.46 mm/ a) before the 1990s but increased significantly (1.57 mm/ a) after the 1990s across China. This phenomenon was closely related to the interdecadal breakpoints in the trends of four meteorological factors affecting ET0 variations. The decrease in ET0 that occurred before the 1990s was attributed to a larger absolute value of the negative contributions caused by decreasing wind speed and sunshine duration compared to that of the positive contribution caused by increasing air temperature. After the 1990s, positive contribution from the air temperature and relative humidity increased due to the more intensive warming and climatic aridity across most of the areas in China and exceeded the smaller absolute value of the negative contribution from the wind speed and sunshine duration, causing the increasing trend in ET0. The interdecadal breakpoints existed at more than 80% of the meteorological stations across China, and there were differences between the pre-and post-breakpoint distribution patterns. Before the 1990s, wind speed and sunshine duration were the determining factors for most stations in North China and South China, respectively. After the 1990s, the number of stations with air temperature or relative humidity as a determining factor increased, especially in Northwest China, the Tibetan Plateau, and some parts of the southeastern coastal area. © 2015 Ecological Society of China. All rights reserved.


Duan C.,Anhui Climate Center | Cao W.,Anhui Meteorological Institute | Cao W.,Anhui Province Atmospheric Science and Satellite Remote Sensing Key Laboratory | Huang Y.,Anhui Meteorological Institute | And 3 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2015

The daily reference evapotranspiration (ET0) is generally demanded in the application of agriculture, meteorology, hydrology and other fields. The calculation of daily ET0 based on the data of different time resolutions is always a simplification because the change of ET0 is a continuous process in the time scale. It is valuable to discuss the influence of the simplification with different time resolutions on the accuracy of ET0 estimation. In this paper, based on the observed data of Shouxian National Climate Observatory from 2007 to 2013, the daily average values were calculated using the data with the resolution of 1 minute as the true values. The effects of the 7 different time resolutions (including 10 min, 20 min, 30 min, 40 min, 60 min, 4 times per day and 3 times per day) on the estimation of daily air temperature, wind speed, solar radiation, relative humidity and daily, monthly, yearly reference evapotranspiration (ET0) were analyzed by the error comparison. Results showed that the absolute values of the errors for ET0 and 4 climatic variables increased with the lower time resolution. Wind speed was most sensitive to the change in the time resolution, followed by solar radiation. The mean absolute relative errors (MAPE) of wind speed were 1.35%, 2.20%, 2.79%, 3.54%, 4.48%, 16.01% and 24.29% for the time resolution of 10 min, 20 min, 30 min, 40 min, 60 min, 4 times per day and 3 times per day, respectively. The change in the time resolution showed less influence on daily air temperature and relative humidity than the other 2 factors. The MAPE values of daily ET0 were 0.53%, 1.01%, 1.38%, 1.72%, 2.46%, 4.72% and 6.14% respectively for the 7 time resolutions, indicating that the accuracies of ET0 estimation for 3 and 4 times per day were significantly lower than the other 5 time resolutions. Over 95% of the absolute errors for daily ET0 with the time resolution from 10 to 40 min were in the range of -0.20-0.20 mm/d. These errors were so small and concentrated that the meteorological data with these 4 time resolutions were suitable for daily ET0 estimation. The mean bias errors (MBE) were almost equal to 0 for the time resolutions from 10 to 60 min, and the total deviation degree was very low. The MBE value for 4 times per day was -0.01 and the estimated ET0 was smaller than the true value, while the MBE value for 3 times per day was 0.02 and the estimated ET0 was larger. The change in the time resolution of the solar radiation led to the largest attribution to the error of estimated ET0, followed by wind speed, because these 2 climatic factors were more sensitive to the change in the time resolution and they were the key factors to the radiation item and dynamic item of ET0 respectively. The absolute values of the errors of monthly and yearly ET0 were significantly less than that of daily ET0. The MAPE values of monthly ET0 were 0.13%, 0.21%, 0.27%, 0.40%, 0.50%, 1.18% and 1.48% respectively for the 7 time resolutions. The absolute values of the relative error of yearly ET0 were mostly less than 0.50%. Our study demonstrated that the change in the time resolution of meteorological variables showed less impact on the estimation of the long-term integrated ET0 and it was important to improve observation time resolution for increasing the ET0 estimation accuracy. ©, 2015, Chinese Society of Agricultural Engineering. All right reserved.


Cao W.,Anhui Meteorological Institute | Cao W.,Anhui Province Atmospheric Science and Satellite Remote Sensing Key Laboratory | Duan C.-F.,Anhui Climate Center | Yao Y.,Anhui Meteorological Institute | And 3 more authors.
Chinese Journal of Applied Ecology | Year: 2014

In this paper, daily reference evapotranspiration (ET0) was computed with the recommended FAO-56 Penman-Monteith equation for Anhui Province using data collected 60 weather stations during 1961 to 2010 and its temporal-spatial variations were characterized. The determining factors in ET0 trends were inquired into through partial derivative quantification analysis for the study region. Results showed that the mean annual ET0 was 878.58 mm • a 1 over the whole region during the study period. ET0 was the highest in summer and the lowest in winter. The mean annual ET0 decreased from the north to the south and from low altitude regions to high altitude regions. Both sunshine duration and wind speed were the dominant factors contributing to the interannual change of ET0, with less contribution from air temperature or relative humidity. The annual ET0 showed a general decline at a rate of -1.61 mm • a-1 owing to a more negative contribution of sunshine duration and wind speed than a positive contribution of air temperature and relative humidity. ET0 increased insignificantly in spring and decreased slightly in both autumn and winter. However, it decreased significantly at a rate of -1.37 mm • a-1 in summer. The main impacting factor was wind speed in spring, autumn and winter, but it was sunshine duration in summer. Great differences in the determining factors of the mean annual ET0 existed from area to area in Anhui Province. The wind speed was the determining factor for 36.7% of the whole stations distributing in the southern part of the area north to the Huaihe River and the area along the Huaihe River, while the sunshine duration was the determining factor for the other regions. ©, 2014, Editorial Board of Chinese Journal of Applied Ecology. All right reserved.


Wu W.,Anhui Meteorological Institute | Wu W.,Anhui Province Atmospheric Science and Satellite Remote Sensing Key Laboratory | Ma X.,Anhui Meteorological Institute | Ma X.,Anhui Province Atmospheric Science and Satellite Remote Sensing Key Laboratory | And 6 more authors.
Nongye Gongcheng Xuebao/Transactions of the Chinese Society of Agricultural Engineering | Year: 2010

The reference crop evapotranspiration is an important component of water resources. For studying its variation under the condition of climate change in Anhui Province, based on the meteorological data observed by 79 meteorological stations of Anhui Province during the period from 1971 to 2005, the values of evapotranspiration were calculated using the Penman-Monteith method recommended by the FAO in 1998. On this basis, a map of reference crop evapotranspiration distribution in Anhui Province was charted using the Kriging interpolation method. The results show that the spatial distribution of annual reference crop evapotranspiration in Anhui Province is strongly affected by many factors, such as the climatic and topographical factors, and the difference of annual reference crop evapotranspiration between the different localities is significant. Generally, it decreases from the northeast to the southwest, which is higher in plain, and lower in mountain. Temporally, it has been in a trend of "fluctuate-decrease" since 1971, and it was the highest at end of 1970 s. Seasonal reference crop evapotranspiration is in a sequence of summer>spring>autumn>winter. Monthly reference crop evapotranspiration is the highest during the period from May to August and lowest during the period from November to next February, while the highest value appears in July, and the difference between the different localilities is also significant.

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