A New Physically-based Pan Evaporation Model and its Application in Explaining Evaporation Paradox and Deriving First Pan Evaporation Reanalysis Dataset in China
Abstract
Pan evaporation (Epan) is the rate of evaporation from a pan and is measured by the change in level of its free water surface. As an integration of meteorological impacts on evapotranspiration, Epan is an important physical indicator of the atmospheric evaporative demand, and its observation network has been established and maintained globally. Unexpected decreasing Epan is reported in many observatory stations under global warming, which is known as the evaporation paradox. In China, many studies observed that evaporation paradox existed from the 1950s to mid-1990s, while disappeared after the mid-1990s.
In the early 2000s, D20 pans were replaced by 601B pans across China, which made it infeasible to analyze the overall Epan trend simply using either D20 or 601B pans. To simulate the missing time series of Epan and explain the overall trend of Epan, we derived a generalized evaporation model, PenPan version 3 (PenPan-V3), for all cylindrical pans. PenPan-V3 is a physically-based model, simulating vapor transfer process between water surface and atmosphere, heat transfer process in boundary layers, and radiation exchange processes on water body and pan walls. We used PenPan-V3 model to simulate Epan across China, capturing the evaporation paradox before the mid-1990s, which mainly results from decreasing wind speed and solar irradiance. Model results also capture the increasing Epan under global warming after the mid-1990s, which is mainly caused by the acceleration of warming and drying. Forced by homogenized and interpolated meteorological data, we ran PenPan-V3 model at monthly time steps for mainland China and generated a continuous and consistent reanalysis dataset for both D20 and 601B pans from 1960 to 2014 at 0.05-degree resolution. The reanalysis dataset can be used to analyze the temporal and spatial distributions of Epan across China, including the areas without observations.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H53K1912W
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 1655 Water cycles;
- GLOBAL CHANGE;
- 1878 Water/energy interactions;
- HYDROLOGY;
- 1880 Water management;
- HYDROLOGY