Mapping global lake dynamics reveals the emerging roles of small lakes

Abstract

Lakes are important natural resources and carbon gas emitters and are undergoing rapid changes worldwide in response to climate change and human activities. A detailed global characterization of lakes and their long-term dynamics does not exist, which is however crucial for evaluating the associated impacts on water availability and carbon emissions. Here, we map 3.4 million lakes on a global scale, including their explicit maximum extents and probability-weighted area changes over the past four decades. From the beginning period (1984–1999) to the end (2010–2019), the lake area increased across all six continents analyzed, with a net change of +46,278 km2, and 56% of the expansion was attributed to reservoirs. Interestingly, although small lakes (<1 km2) accounted for just 15% of the global lake area, they dominated the variability in total lake size in half of the global inland lake regions. The identified lake area increase over time led to higher lacustrine carbon emissions, mostly attributed to small lakes. Our findings illustrate the emerging roles of small lakes in regulating not only local inland water variability, but also the global trends of surface water extent and carbon emissions.

Contemporary and historical detection of small lakes using cross-sensor super resolution Landsat imagery

“…Using airborne camera imagery Kyzivat et al (2019b) find an onset of power law behavior at 343,074 m 2 , which is in general agreement with our results of 536,738 to 698,115 m 2 (Table 3). This size limit is within the range of MMUs of 3,600 m 2 -30,000 m 2 (4-33 pixels) from previous studies (Pekel et al 2016, Kyzivat et al 2019bMuster et al 2019;Sui et al 2022;Verpoorter et al 2014;Paltan et al 2015;Pi et al 2022) and well above our own recommendation of 2 /3 of a pixel for SR Landsat imagery. This high size limit indicates that the onset of power law behavior is a true geophysical phenomenon, not an artifact of sensor resolution.…”

“…Raster map products like the Global Surface Water (GSW) suite (Pekel et al 2016) use a minimum mapping unit (MMU) of one Landsat pixel, but a single water pixel is not guaranteed to be a lake. Vector classifications, which delineate discrete water bodies as objects typically have an MMU of several pixels, such as 40 pixels (40 m 2 ) for airborne camera imagery (Kyzivat et al 2019b;Muster et al 2019); 10 pixels (1,000 m 2 or 0.001 km 2 ) for Sentinel-2 (Sui et al 2022); 9 pixels (0.002 km 2 ) for pansharpened Landsat 7 (Verpoorter et al 2014); 4 pixels (0.0036 km 2 ) for Landsat 8 (Paltan et al 2015); and 33 pixels (0.03 km 2 ) for combined Landsat (Pi et al 2022) imagery. While convention requires an MMU of 4-33 Landsat pixels (3,600 -8,100 m 2 ), such limits, in practice, still undercount small lakes, with high-resolution mapping showing that 70% of sampled northern lakes are smaller than 4 pixels and would thus be excluded (Kyzivat et al 2018(Kyzivat et al , 2019a.…”

Decreasing relative importance of drawdown areas on waters in CO2 emissions in drylands

“…Global climate change has led to more melting of glaciers, decline of winter RS and LR ice sheets 45,46,47,48 , and increase in the number of human-controlled reservoirs 49 , thus resulting in the expansion of waters in parts of the world over the past decade, especially in drylands, where waters is closely related to surface runoff from glacial melting 9,50 .The expansion of total waters area of RS and LR in drylands is the main reason for the increase of CO2 emissions from waters. Notably, the increase rate of waters in temperate was higher than that in tropical, indicating that waters in temperate drylands are more responsive to climate change 51 .…”

Global mapping reveals more intensively exploited inland than coastal wetlands

“…3) 42,45 . We further estimated the proportion of reclaimed inland wetlands in lakes, using lake boundaries as de ned in the GLAKES dataset 46 ; GLAKES provides the maximum extent of > 3 million lakes with a surface area > 0.03 km 2 .…”