The Urgency of Studying Lake Processes and Their Climate Effects Under Global Warming

1. Introduction

Lakes are sensitive indicators of climate change, playing a critical role in hydrological cycles and ecological functions [1]. Natural lakes comprise approximately 304 million lakes globally, covering a total area of 4.2 million km² [2]. Of these, there are approximately 3.4 million lakes larger than 0.03 km² [3]. Small water bodies dominate in terms of number, whereas lakes larger than 1 km² amount to around 155,000, collectively spanning an area of approximately 2.3 million km². Lakes and reservoirs in the United States cover an area of 131,000 km² [4], while the Tibetan Plateau (TP) boasts more than 1400 lakes larger than 1 km², forming the world’s largest high-elevation endorheic lake zone [5]. Under global warming, key lake attributes—such as area [6], level [7], volume [8,9], turbidity, and transparency—along with meteorological and hydrological variables, lake-atmosphere turbulent fluxes (e.g., evaporation, sublimation, and greenhouse gas exchanges) [10,11,12], and lake ice phenology [13] have undergone significant changes. These variations differ across climatic regions. For instance, due to elevation-dependent warming over the TP, the high-elevation lakes are expanding in number, area, and water level, intensifying the regional hydrological cycles [14,15]. Projections further suggest that lake levels and areas could rise by over 10 m and expand by more than 50% by 2100 [16]. In contrast, lakes in arid regions are shrinking due to heightened evaporation, excessive irrigation, declining precipitation, and cryosphere meltwater [17]. These hydrological shifts alter the land surface conditions, affect lake–land thermal contrasts [18], modify lake–land breeze circulations [19], and impact cloud formation and precipitation patterns [20,21,22].

Under global climate warming, lakes generally exhibit trends such as shortened ice ages, accelerated surface warming, and prolonged summer thermal stratification periods [23]. Climate warming is also altering lake mixing regimes. Many lakes are transitioning from dimictic to monomictic, while some perennial lakes are becoming seasonal or even ice-free [24,25,26]. Intensified stratification is increasing anoxia and hypoxia events, which were once primarily winter phenomena, but are now more frequent in summer, leading to severe ecological consequences such as fish die-offs and ecosystem disruptions [27]. Lakes and land surfaces exhibit significant differences in their physical properties. When cold air moves over warm water bodies, the lower atmosphere absorbs large amounts of water vapor and heat, creating favorable conditions for the formation of strong convective cloud clusters. This process can potentially trigger local lake–land breeze circulations, exerting a significant influence on the regional weather and climate [28,29]. Given these transformations, the systematic monitoring of hydrological, meteorological, and ecological changes in global lakes is essential. Comprehensive studies integrating in situ measurements, satellite observations, and numerical simulations are critical for understanding evolving lake systems and their broader climatic and ecological implications.

To address these concerns, a Special Issue entitled “Lake Processes and Their Climate Effects under Global Warming” in Water was initiated by Professor Yaoming Ma and Professor Binbin Wang from the Institute of Tibetan Plateau Research, Chinese Academy of Sciences; Professor Jiming Jin from Yangtze University; and Professor Lijuan Wen from the Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences. This Special Issue focused on the measurements and simulations of lake processes and hydrological cycles within lake catchments, including lake surface temperature, ice phenology, evaporation and sublimation estimates, and changes in lake level and volume. It highlights advancements in lake monitoring through in situ measurements, satellite data (visible, thermal, and microwave bands), and numerical simulations. As of 20 September 2024, this Special Issue was concluded with a total of nine published papers. A summary of their key findings is provided below.

2. Main Contributions of the Special Issue

In situ measurements of lake processes remain limited due to the challenges of establishing observation sites and conducting field experiments on lakes. Consequently, a key focus of the Special Issue has been focusing on enhancing lake process measurements. Wang et al. (2023) investigated lake stratification and mixing processes in both large and small high-elevation lakes across the TP. They identified significant diurnal and seasonal variations in epilimnion depth, driven by different factors; in large lakes, turbulent heat flux and radiation flux dominate, whereas in small lakes, radiation flux and wind speed play leading roles (Contribution 1). Aslamov et al. (2024) analyzed the mesothermal temperature maximum layer (MTML) in Lake Baikal, revealing that wind conditions significantly influence MTML depth (Contribution 2). During cold seasons, as wind activity intensifies in late fall, the MTML deepens and its temperature decreases. In contrast, during other periods, the MTML remains closer to the surface with higher temperatures. Zheng et al. (2023) examined inter-annual and intra-annual water level changes, reporting a decline of 0.8 m per decade from 1956 to 2004 and an increase of 1.7 m per decade, respectively. They attributed the initial decline to higher evaporation rates exceeding precipitation and runoff, while the subsequent rise was driven by increased precipitation and runoff (Contribution 3).

Another key research direction involves numerical simulations for monitoring lake variations. Si et al. (2023) studied ice freezing and melting processes by integrating a one-dimensional physics-based model with in situ measurements. By incorporating air density, lake water salinity, and ice sublimation, the model improved simulations of lake surface temperature, ice thickness, and ice phenology (Contribution 4). Cao et al. (2023) enhanced the Flake model’s performance for small- to medium-sized lakes by optimizing the water extinction coefficient, friction velocity, and ice albedo, significantly reducing the simulation bias and RMSE values. Incorporating a salinity scheme further improved the simulated thermal structure. Hydrological models have also been used to study catchment water cycles (Contribution 5). Tang et al. (2023) investigated the inflow sources of Yamzho Yumco using a distributed hydrological model. From 1974 to 2019, the average runoff into the lake was 5.5 ± 1.4 × 10⁸ m³ per decade, with contributions from rainfall runoff (54.6%), base flow (32.7%), glacier melt runoff (10.8%), and snowmelt runoff (1.8%) (Contribution 6). Most runoff occurred during warm seasons, with contributions from spring and winter comprising less than 10%. Cui et al. (2023) analyzed the hydrometeorological changes in the Ranwu Lake basin in the southeastern part of the TP, observing significant warming and declining precipitation. Glacier meltwater accounted for 54% of the total runoff, while snowmelt, rainfall, and base flow contributed 23%, 12%, and 11%, respectively (Contribution 7). Due to accelerated glacier retreat, the total runoff is expected to decline further, with only one-fifth of glaciers remaining by 2100.

The last research direction is climate change-related environmental and public health challenges, given their influence on water quality and availability. Ayele (2024) reviewed the historical, current, and projected impacts of climate change on water resources in the Murray–Darling Basin, Australia, highlighting the increasing frequency of blue–green algae blooms and blackwater events (Contribution 8). Nachtigall and Heim (2023) assessed restoration efforts for the shallow, eutrophic Lake Seeburg in central Germany, including riverbed prolongation, gradient reduction, and upstream wetland construction (Contribution 9). Despite these measures, the lake remains a nitrogen sink, with phosphorus fluxes showing a negative balance in winter and a positive balance in summer. Upstream wetlands release large amounts of phosphorus, further contributing to eutrophication.

3. The Perspective for Future Directions

Global warming has led to the widespread warming and wetting of lake catchments, with increased precipitation and evaporation. In cold, glacier-dominated catchments, lake numbers, areas, and volumes are expanding due to higher precipitation, accelerated glacier retreat, and continuous permafrost melt. In contrast, lakes in arid regions are shrinking due to intensified evaporation and limited water replenishment. Climate extremes, including droughts and floods, are becoming more frequent, posing risks to communities and ecosystems. Additionally, extreme ice-free years are increasing in frequency and severity, leading to significant ice loss. Reduced lake ice growth is projected in the coming decades, affecting hundreds of millions of people and underscoring the urgency of climate mitigation strategies [24,25].

Future lake research should integrate in situ measurements, satellite data, numerical simulations, and field experiments to address the knowledge gaps in lake dynamics and their responses to climate change [30]. Advancing new technologies (e.g., dual-band scintillometers, unmanned survey vessels, etc.) and fostering interdisciplinary collaborations will enhance our understanding of lake processes and their impacts on the weather and climate across broad spatial and temporal scales. The following four directions should be emphasized.

(1)

Regional hydroclimate variations

Special attention is needed to understand regional climate variations across lake basins. Hydrological changes vary between dry and high-elevation cold regions, requiring a deeper understanding of how increased evaporation and reduced replenishment affect inland arid lakes and how glacier meltwater drives lake expansion in high-altitude regions such as the TP. These insights will help reveal the diverse patterns of lake evolution across various climates.

(2)

Climate change, extreme events, and lake–climate feedbacks

Climate change will alter regional weather and climate patterns, particularly regarding extreme events and lake–climate interactions. Understanding how lake regulation and storage functions degrade (e.g., in arid regions) or intensify (e.g., in cold regions) is crucial for assessing their effects on flood and drought risks. Additionally, as glacial lakes increase due to enhanced glacier melt, predictive models are needed to assess glacial lake outburst flood risks and their impacts on downstream ecosystems and infrastructure. Research should also focus on identifying algal bloom response thresholds to warming and nutrient inputs in different regions and developing targeted mitigation strategies based on climate scenarios.

(3)

Lake drainage, carbon fluxes, and ecological impacts

Lake drainage events influence organic carbon fluxes and may contribute to climate system feedbacks. It is crucial to identify habitat fragmentation hotspots due to lake shrinkage or expansion and establish species migration protection plans based on ecological corridors. Integrating remote sensing with hydrological models will improve water level fluctuation predictions for high-altitude and high-latitude glacial lakes, aiding disaster early-warning systems.

(4)

Policy integration and public awareness

Climate change will alter land surface conditions and affect lake–land breeze circulation, influencing pollutant diffusion in nearby cities. Additionally, warming will impact lake stratification and mixing, increasing the frequency of anoxia and hypoxia events, which threaten fishery resources. Therefore, raising public awareness of lake protection and implementing effective policies are essential for conservation efforts and the well-being of local communities.