New Dataset of Global Evaporative Water Loss

Evaporative water loss of 1.42 million global lakes

Gang Zhao, Yao Li, Liming Zhou and Huilin Gao

Summarized by Michael Hallinan 

What data was used?  A series of geospatial data containing information on global lakes that are over 0.1 square kilometers (approximately 328 square feet) was sourced from HydroLAKES, a database centered around mapping the global freshwater. The data included a total of 1,427,688 water bodies, of which 6715 are reservoirs. In addition to this, three sets of meteorological data from TerraClimate, ERA5, and GLDAS were used to cancel bias as each dataset was developed independently through different institutes with a wide range of input sources. Lastly, a series of lake ice coverage and lake evaporation data were obtained from the Natural Snow and Ice Data Center and previous studies, respectively. 

Methods: Using the geospatial data on lakes, a series of calculations was performed to estimate potential water loss due to evaporation of lakes and reservoirs. This was performed through calculating the change in heat stored by the body of water using the density, specific heat of water, water depth, and change in water temperature. Then an estimation of lake evaporation rate was performed using vapor pressure, net radiation, change in heat, surface area, as well as wind and other environmental data. In addition to this, further data processing occurred to account for ice coverage as well as to remove biases in satellite-sourced data caused by cloud coverage.  

Results: This study created a dataset of evaporative water loss from 1958 to 2018 containing estimates of monthly evaporative loss of over 1.42 million lakes world wide. The most notable observations of this dataset are that the long-term average global lake evaporation has increased by 3.12 cubic kilometers per year in volume (roughly 0.75 cubic miles) while the average currently is 1500±150 cubic kilometers (roughly 932 cubic miles). This trend is likely a result of three main factors: Around 58% of this increase is a consequence of increased evaporation rate, 23% is caused by decreasing lake ice coverage, and 19% stems from an increase in lake surface area. In addition to this, these three factors have an identifiable pattern in their global distribution. High-latitude and high-altitude regions such as Tibetan Plateau and northern Eurasia show amplified effects of climate change on ice duration and as a result evaporation, likely having accelerated evaporation in the future.

Global map showing a ratio of lake evaporation versus total evapotranspiration (all land evaporation plus plant transpiration, with values ranging from 0% to >30%. Most of the global land surface falls into the 3% to 6% range. Much of Canada as well as some of the western regions of the United States fall into the 6% to 10% range, with some regions of Canada being in the 10% to 18% or even 18% to 30% range. The northern region of South America is predominantly between 0 and 1% while the southern hemisphere is mainly between 3% and 6% with some regions near the upper Andes Mountains having a ratio of 18 to 30%. Africa is a mix with much of the continent varying between 0 to 1% and 3 to 6% with some of the southern and north-eastern regions having ratios between 6 to 10% and even >30% near Egypt. This is globally the area with the highest ratio. Eurasia is mainly between the 0 to 1% and 1 to 3% categories with the exception of Iraq and Iran with that region having 6 to10% up to 18 to 30% ratios appear. InFinland, Europe also begins to see this same ratio increase to 6 to 10% and 10 to 18%. Lastly, Oceania is a mix of 1 to 3% and 0 to 1% with the 0 to 1% occurring on the eastern side of Australia and the majority of the island nations.
Global map showing percentage ratio of lake evaporation versus total evapotranspiration (all land evaporation plus plant transpiration).

Why is this study important? This dataset is essential to understanding global evaporative loss and the response of bodies of water to global warming. This dataset is the first of its kind to provide long-term monthly evaporation data on a global scale. This information can be used in the context of water availability estimations as well as in climate models. Although previous studies about water evaporation have been performed, many of them focused on only a few environmental parameters such as lake surface temperature, lake and river ice, or other attributes. This knowledge will be imperative in improving our overall understanding of the effects of lake evaporation

The big picture: A dataset of evaporation data comprising 1.42 million lakes from 1958 to 2018 was formed through a mixture of geospatial, meteorological, and lake ice coverage data. This dataset is the first of its kind and can be used to better understand water availability as well as water bodies’ reaction to climate change. Lastly, through this dataset it was discovered that there is an increase in water evaporation of about 3.12 cubic kilometers per year in volume (roughly 0.75 cubic miles).

Citation: Zhao, G., Li, Y., Zhou, L. et al. Evaporative water loss of 1.42 million global lakes. Nat Commun 13, 3686 (2022).

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