Lake surface temperatures in a changing climate: a global sensitivity analysis

We estimate the effects of climatic changes, as predicted by six climate models, on lake surface temperatures on a global scale, using the lake surface equilibrium temperature as a proxy. We evaluate interactions between different forcing variables, the sensitivity of lake surface temperatures to these variables, as well as differences between climate zones. Lake surface equilibrium temperatures are predicted to increase by 70 to 85 % of the increase in air temperatures. On average, air temperature is the main driver for changes in lake surface temperatures, and its effect is reduced by ~10 % by changes in other meteorological variables. However, the contribution of these other variables to the variance is ~40 % of that of air temperature, and their effects can be important at specific locations. The warming increases the importance of longwave radiation and evaporation for the lake surface heat balance compared to shortwave radiation and convective heat fluxes. We discuss the consequences of our findings for the design and evaluation of different types of studies on climate change effects on lakes.     

Long-term Changes in the Main Components of Lake Khanka Water Regime

Changes in annual total precipitation and annual pan evaporation for the Lake Khanka water area during the period of 1949–2015 are analyzed based on observational data of weather stations within the lake basin. The reliability of the calculated values of characteristics affecting evaporation changes was confirmed by their comparison with observations at the 20-m² evaporation pan installed at Astrakhanka lake station. It is shown that against a background of significant interannual fluctuations of annual precipitation during the whole period under study, its trends are almost absent. However, a rather stable increase in annual precipitation value caused by the summer precipitation rise has been noted since the early 2000s. The value of annual pan evaporation decreased from 1949 to 2015, and the rate of its decrease till 1980 was higher than in the next period. Moreover, some evaporation increase has been observed in the recent decade. The main contribution to the evaporation change is made by wind speed changes which cause about 50% of evaporation variance. Air humidity deficit is the second affecting factor that determines a little over 20% of annual evaporation variance. It is demonstrated that the increase in annual precipitation is possible by the middle of the 21st century, while the change in annual evaporation from the Lake Khanka water area would be minimal. Under such changes in the main components of the lake water regime, no reduction of its level due to natural climate processes should be expected.     

The significance of surface temperature patterns on the energy balance of a small lake in the Canadian Shield

Abstract

Temperature patterns of a small lake in the Canadian Shield are examined by means of thermal imagery. The effect of the different surface temperatures on the daytime energy balance is examined for two points over the lake at the time the thermal imagery was taken. For 14 June 1979, two distinct energy balance regimes are noted. At the lake centre, where the deeper water registers a relatively cool thermal signature, a boundary‐layer inversion is observed. The downward sensible heat flux augments the net radiation, and the latent heat flux is 105% of the radiant input. Along the lake margins, the shallows register warm thermal signatures and a lapse profile is observed. The sensible heat flux is an energy sink and the latent heat flux is diminished to 88% of the net radiation. This difference indicates that a single point estimate may introduce a bias if it is assumed to be representative of the lake average for the purposes of studying lake evaporation.

The calculation of the latent heat flux and evaporation is very sensitive to the value of the surface temperature. When the spatial patterns of surface temperature are considered in an estimate of the lake evaporation, the spatially integrated value differs by —6% from the estimate based upon a single point observation at the lake centre for a mid‐day in June and by +10% from the estimate based upon observations collected over the warm shallows.     

2002-2017年扎日南木错湖面面积变化分析

利用2002～2017年MODIS数据,结合3个气象站观测资料,分析扎日南木错2002～2017年湖面变化以及气象要素之间相关性。分析表明;近15年来扎日南木错湖泊水域面积整体呈波动上升趋势,从空间分布来看,扎日南木错的西部和北部湖面扩张的比较明显,尤其是北部有个小岛,可以看到从小岛形成到消失过程。气温整体呈上升趋势,降水量和蒸发量呈下降趋势,湖泊水域面积变化与气温呈正相关,蒸发量和降水量呈负相关。      

Multiple factors causing Holocene lake-level change in monsoonal and arid central Asia as identified by model experiments

Lake-level records provide a rich resource of information about past changes in effective moisture, but water-balance fluctuations can be driven by a number of different climate variables and it is often difficult to pinpoint their exact cause. This understanding is essential, however, for reconciling divergent paleo-records or for making predictions about future lake-level variations. This research uses a series of models, the NCAR CCSM3, a lake energy-balance and a lake water-balance model, to examine the reasons for lake-level changes in monsoonal Asia and arid central Asia between the early (8.5 ka), middle (6.0 ka) and late (ca. 1800 AD) Holocene. Our results indicate that the components of the lake water balance responsible for lake-level changes varied by region and through time. High lake levels at 8.5 and 6.0 ka in the monsoon region were caused by the combined effects of low lake evaporation and high precipitation. The low lake evaporation resulted from low winter solar radiation and high summer cloud cover. Precipitation associated with the mid-latitude westerlies increased from the early to middle Holocene and maintained high lake levels throughout most of arid central Asia ca. 6 ka. The modeled evolution of lake level in arid central Asia from the mid to late Holocene was spatially heterogeneous, due to different sensitivities of the northern and southern parts of the region to seasonally-changing insolation, particularly regarding the duration of lake ice cover. The model results do not suggest that precipitation and lake evaporation changes compete with one another in forcing lake-level change, as has been hypothesized.     

Soil occupation and atmospheric variations over Sobradinho Lake area. Part two: a regional modeling study

Summary The impact of the changes on soil cover and land use brought about by the construction of the Sobradinho Dam in the semi-arid region of the S?o Francisco River Hydrographic Basin is analyzed by means of a numerical model RAMS. Disregarding the influence of a large scale flow, a set of factors were responsible for the creation of a rather complex circulation system that includes mountain-valley winds, lake breeze (LB) and non-conventional circulation all induced by the surface non-homogeneous aspect. Results have demonstrated that the implementation of works of such magnitude brings about environmental changes in an area that stretches far beyond the surroundings of the reservoir. The soil cover alterations due to the ever increasing development of the area with the presence of irrigated crops in a sparsely vegetated region (caatinga) does affect land surface characteristics, occasioning for that matter the splitting of the available energy into latent and sensible heat fluxes. LB behavior varies in accordance with atmospheric conditions and also in view of the type of vegetation found in the lake surrounding areas. Hydro availability in root zones, even under adverse atmospheric conditions (high temperature and low air humidity) brings up the high rates of evaporation and plant transpiration that contribute towards the increase of humidity and the fall of temperature in lower atmospheric layers.     

Effects of salinity upon evaporation from pans and shallow lakes near the Dead Sea

Summary Evaporation was evaluated for three shallow lakes near the Dead Sea with specific gravities (s.g.) of 1.26, 1.31 and 1.34, and for a hypothetical fresh lake of similar depth. The annual march of lake temperature was adequately predicted with an equilibrium temperature model. Predicted temperatures were only slightly affected by neglecting heat exchange between the lake and the underlying sediments. Modeled lake temperatures were then used in a modified Penman-type model and an alpha ratio model to generate evaporation estimates. The evaporation models were verified by comparison against 1950'ies water balance estimates of evaporation from the Dead Sea (s.g. about 1.18). Annual totals of evaporation predicted by the models for the shallow lakes declined from 2125 mm for fresh water (s.g. = 1.0) down to 588 mm for the most saline conditions (s.g. = 1.34). Evaporation was also measured from sunken pans in which s.g. was maintained at 1.0, 1.26, 1.31 and 1.34. Mean monthly pan coefficients (from lake/pan evaporation for equal s.g. values) ranged from 0.63 up to 1.03 as s.g. increased from 1.00 up to 1.34. The variations in coefficients are attributed to effects of salinity on the mechanisms that control the gain and loss of heat to the ponds and evaporation pans. The temperatures of the saline lakes were always somewhat warmer than the temperatures measured in the sunken pans, ranging from + 0.7 °C for s.g. of 1.26 up to + 1.3 °C for s.g. of 1.34; the corresponding value for the fresh condition was — 0.4 °C. The pan coefficients defined here for saline conditions will be useful for estimating actual water loss from brine-filled ponds used in commercial extraction of potash and other chemicals.With 2 Figures     

Evaporation estimates from Nasser Lake, Egypt, based on three floating station data and Bowen ratio energy budget

Nasser Lake is located in a hyper-arid region in the south of Egypt. Evaporation is by far the most important factor in explaining the water losses from the lake. To obtain better management scenarios for Nasser Lake, an accurate estimation of the lake evaporation losses thus is essential. This paper presents an update of previous evaporation estimates, making use of local meteorological and hydrological data collected from instrumented platforms (floating weather stations) at three locations on the lake: at Raft, Allaqi, and Abusembel (respectively at 2, 75, and 280 km upstream of the Aswan High Dam). Results from six conventional evaporation quantification methods were compared with the values obtained by the Bowen ratio energy budget method (BREB). The results of the BREB method showed that there is no significant difference between the evaporation rates at Allaqi and Abusembel. At Raft, higher evaporation rates were obtained, which were assumed to be overestimated due to the high uncertainty of the Bowen ratio (BR) parameter. The average BR value at Allaqi and Abusembel was used to eliminate this overestimates evaporation. Variance-based sensitivity and uncertainty analyses on the BREB results were conducted based on quasi-Monte Carlo sequences (Latin Hypercube sampling). The standard deviation of the total uncertainty on the BREB evaporation rate was found to be 0.62 mm day^?1. The parameter controlling the change in stored energy, followed by the BR parameter, was found to be the most sensitive parameters. Several of the six conventional methods showed substantial bias when compared with the BREB method. These were modified to eliminate the bias. When compared to the BREB-based values, the Penman method showed most favorably for the daily time scale, while for the monthly scale, the Priestley–Taylor and the deBruin–Keijman methods showed best agreement. Differences in mean evaporation estimates of these methods (against the BREB method) were found to be in the range 0.14 and 0.36 mm day^?1. All estimates were based calculations at the daily time scale covering a 10-year period (1995–2004).     

1988—2018年那曲市其香错水域面积变化及原因分析

基于Landsat卫星遥感数据,采用水体指数法和相关分析法,分析1988—2018年那曲市双湖县其香错湖泊水域面积变化及原因。结果表明：该湖泊近31 a内水域面积呈显著增长趋势（R²=0.88,P < 0.001）,31 a内增长了33.37 km²,增长率为18.03%;从空间上分析,其香错在近31 a内湖泊面积不断向四周扩展,其中在东、西方向和北部变化尤为显著。湖泊所在区域年平均气温呈增加趋势,蒸发量显著减小,冻土深度也明显减小。在上述因素的共同作用下,引起湖泊补给水源的增加和湖泊水容量的增大,最终导致湖泊面积持续上涨。     

Role of exchange flow in salt water balance of Urmia Lake

In this paper we examine how exchange flow in Urmia Lake plays a crucial role in dynamics of the lake. Urmia Lake, a very large hyper-saline lake of high ecological significance, is located in northwest of Iran with a 15-km causeway dividing it into north and south lakes. A 1250-m opening in the causeway near the east coast links the two lakes. The differences in mean water levels and densities of the two lakes increase in spring due to large freshwater inflows into the south lake. High evaporation dominates the lake in summer. By incorporating the results of a two-layer hydraulics theory into a mixing model of the lake, we show that the exchange flow through the opening diminishes the water level and salinity differences of the two lakes and hence helps restoration of the pre-construction state of the lake by the end of fall. The model results are confirmed by the field data. The north–south and south–north flows through the opening are equal in most of the year, except in spring when the south–north flow is greater due to the head difference of the two lakes.     

Evaluation of the Climatic Change Impacts on the Inland Lake – A Case Study of Lake Qinghai, China

A catchment model coupled with a lake thermal model has been used to simulate the lake water balance of Lake Qinghai, a large inland lake on the northeast Qinghai-Tibet Plateau in China. The sensitivity analyses show that changes in precipitation will produce larger changes in runoff than temperature and cloudiness, whereas changes in lake level are equally sensitive to changes in temperature and precipitation. With a doubling of CO₂ in the atmosphere, four GCMs experiments predict warmer and wetter conditions in the Qinghai region than at present. The total runoff in the lake basin and evaporation will, in most cases, increase as conditions become warmer and wetter. The lake level changes would remain uncertain because the effects of an increase in precipitation are countered by the rise of temperature.     

The influence of a water surface on mesoscale dynamics as a function of atmospheric stability

Several numerical experiments have been undertaken with a three-dimensional mesoscale model in order to determine to what extent a water surface such as a lake can influence mesoscale flow patterns.It is shown that the influence of the lake is important when cumulus clouds are present. These clouds, generated by evaporation from the water surface are small but induce significant secondary circulations which disrupt the flow field on the mesoscale.Artificial suppression of cloud activity results in a situation where the lake exerts little influence on the atmospheric environment in comparison to the control experiment where the body of water is absent. Atmospheric stability controls the intensity of perturbations to the mean flow when clouds are present.The study is of interest when modeling a number of complex phenomena simultaneously; the results shown here indicate that under certain stability conditions, a small lake can be ignored as to its dynamic and thermodynamic influence on atmospheric processes, thus leading to a neglect of a number of equations taking into account moisture terms explicitly.     

The estimation of the energy balance of a lake from simple weather data

The energy balance of a lake with an area of approximately 46000 ha and a depth of 3 m has been estimated from simple weather data measured along the perimeter of the lake. These measurements are dry-bulb temperature and relative humidity, both at 1.5-m height, windspeed at 3-m height and sunshine duration. The estimated energy balance values were compared with the values computed from the measurements at the station situated at the centre of the lake. At this station, net radiation, water temperature, dry-bulb and wet-bulb temperature at a height of 2 m were measured. It is possible to estimate the daily evaporation from the lake with an error of 0.6 mm day^–1, if the location of measurement is downwind from the lake.     

基于MODIS影像的西藏羊卓雍湖面积变化与成因分析

分析2002~2009年MODIS卫星数据和2000~2009年气象数据分析可得:西藏羊卓雍湖面积在近8年呈显著减小趋势,8年内面积减小了96.61km2;湖泊所在的浪卡子气象站气温、地表温度呈升高趋势,降水量、相对湿度呈减少趋势。在降水量减少、气温升高的情况下由于降水量减少的幅度要远大于蒸发量的减少,是2000~2009年内湖泊面积下降的主要原因之一;本研究也证明了MODIS资料可以作为研究湖泊面积变化的补充数据源。      

Simulation of lake ice and its effect on the late-Pleistocene evaporation rate of Lake Lahontan

A model of lake ice was coupled with a model of lake temperature and evaporation to assess the possible effect of ice cover on the late-Pleistocene evaporation rate of Lake Lahontan. The simulations were done using a data set based on proxy temperature indicators and features of the simulated late-Pleistocene atmospheric circulation over western North America. When a data set based on a mean-annual air temperature of 3° C (7° C colder than present) and reduced solar radiation from jet-stream induced cloud cover was used as input to the model, ice cover lasting 4 months was simulated. Simulated evaporation rates (490–527 mm a^–1) were 60% lower than the present-day evaporation rate (1300 mm a^–1) of Pyramid Lake. With this reduced rate of evaporation, water inputs similar to the 1983 historical maxima that occurred in the Lahontan basin would have been sufficient to maintain the 13.5 ka BP high stand of Lake Lahontan.     

Response of inland lake dynamics over the Tibetan Plateau to climate change

The water balance of inland lakes on the Tibetan Plateau (TP) involves complex hydrological processes; their dynamics over recent decades is a good indicator of changes in water cycle under rapid global warming. Based on satellite images and extensive field investigations, we demonstrate that a coherent lake growth on the TP interior (TPI) has occurred since the late 1990s in response to a significant global climate change. Closed lakes on the TPI varied heterogeneously during 1976–1999, but expanded coherently and significantly in both lake area and water depth during 1999–2010. Although the decreased potential evaporation and glacier mass loss may contribute to the lake growth since the late 1990s, the significant water surplus is mainly attributed to increased regional precipitation, which, in turn, may be related to changes in large-scale atmospheric circulation, including the intensified Northern Hemisphere summer monsoon (NHSM) circulation and the poleward shift of the Eastern Asian westerlies jet stream.     

Great Lakes Hydrology Under Transposed Climates

Historical climates, based on 43 years of daily data from areas south and southwest of the Great Lakes, were used to examine the hydrological response of the Great Lakes to warmer climates. The Great Lakes Environmental Research Laboratory used their conceptual models for simulating moisture storages in, and runoff from, the 121 watersheds draining into the Great Lakes, over-lake precipitation into each lake, and the heat storages in, and evaporation from, each lake. This transposition of actual climates incorporates natural changes in variability and timing within the existing climate; this is not true for General Circulation Model-generated corrections applied to existing historical data in many other impact studies. The transposed climates lead to higher and more variable over-land evapotranspiration and lower soil moisture and runoff with earlier runoff peaks since the snow pack is reduced up to 100%. Water temperatures increase and peak earlier. Heat resident in the deep lakes increases throughout the year. Buoyancy-driven water column turnover frequency drops and lake evaporation increases and spreads more throughout the annual cycle. The response of runoff to temperature and precipitation changes is coherent among the lakes and varies quasi-linearly over a wide range of temperature changes, some well beyond the range of current GCM predictions for doubled CO₂ conditions.     

The water and energy balances of Perch Lake (1969–1980)

Abstract

Since 1969, meteorological and limnological measurements required for evaporation estimates by the energy budget method have been made almost continuously during the open water season at Perch Lake, a small (0.45 km²), shallow (mean depth 2 m) lake on the Canadian Shield. Hydrological measurements required for water budget calculations have been made continuously since 1970. Since ground water input to the lake has been found to be significant, energy budget estimates of evaporation are used in the water budget equation to estimate ground water inflow. Results are summarized as the long‐term averages along with the ranges of variation of the budget components observed during the eleven‐year period.     

Transposed Climates for Study of Water Supply Variability on the Laurentian Great Lakes

Hydrological models of the Great Lakes basin were used to study the sensitivity of Great Lakes water supplies to climate warming by driving them with meteorological data from four U.S. climate zones that were transposed to the basin. Widely different existing climates were selected for transposition in order to identify thresholds of change where major impacts on water supplies begin to occur and whether there are non-linear responses in the system. The climate zones each consist of 43 years of daily temperature and precipitation data for 1,000 or more stations and daily evaporation-related variables (temperature, wind speed, humidity, cloud cover) for approximately 20–35 stations. A key characteristic of these selected climates was much larger variability in inter-annual precipitation than currently experienced over the Great Lakes. Climate data were adjusted to simulate lake effects; however, a comparison of hydrologic results with and without lake effects showed that there was only minor effects on water supplies.     

Air-sea interaction including a shallow and coastal zone

We performed special experimental and theoretical research concerning the energy--mass exchange process in shallow waters, which took into account the influence of the basin depth on the evaporation and sensible heat exchange. Data was obtained from deep water basins, as well as from shallow waters, at an open sea, as well as in its coastal zone. A new parameterization model of evaporation and friction velocity from shallow water surfaces under different wind velocities was investigated. Results of models and measurements of the energy/mass exchange intensity of a small shallow lake (LITFASS-experiments) were compared. The validation of these models with the eddy-covariance measurements of the LITFASS-98 and LITFASS-2003 experiments showed good results for the wind sector, with good fetch conditions. Therefore, the models examined may be used for calculating the evaporation of lakes where a standard data set of wind velocity, air and water temperature, air moisture and the depth of the lake is available. It should be remembered that in a coastal zone the roughness of the water surface is transformed and therefore there are additional calculation difficulties for the intensity of the energy-mass exchange. Based on our experimental data of the basin depth influence on the water-atmosphere exchange, a new model for the calculation of the energy-mass exchange in a coastal zone was developed. Our new model in combination with the empirical dependence for the calculation of the energy-mass exchange in a coastal zone allows calculation of the momentum, heat and humidity fluxes values at different distances from a shore.