Lake-land Breeze Research Articles

Modelling analysis of the potential impact of large reservoir on heatwave events

The impact of large reservoirs on regional climate extremes, such as heatwaves, is not yet well understood, primarily due to the complex interactions of heat, moisture, and momentum over mountainous terrains and the dynamic nature of water surfaces. In this study, we investigate the role of the Miyun Reservoir (MYR), one of the largest reservoirs in northern China, covering an extensive water surface area of 180 km2, in influencing a severe heatwave event that occurred southwest of MYR from 2nd to 6th July 2010. Using high-resolution simulations from the Weather Research and Forecasting Model, our findings reveal contrasting thermodynamic effects of MYR on near-surface air temperatures, with up to three degrees of warming during night-time and up to five degrees of cooling during daytime, with a spatial extent of impact reaching up to 20 km away from the reservoir. These impacts are attributed to a combination of synergized land-lake breeze and mountain-valley winds during the night, leading to the transport of warm air plumes downwind towards the plain and intensifying the heatwave. Furthermore, we observe an increase in surface water vapor brought to higher atmospheric levels due to strong vertical mixing, resulting in lowered surface-specific humidity. Our study emphasizes the dual role of large reservoirs in exacerbating remote heatwaves while providing cooling effects in their proximity. Gaining a comprehensive understanding of the intricate interactions between reservoirs, topography, and regional climate extremes is of paramount importance for accurate climate risk assessments and the formulation of effective mitigation strategies..

A strong short-duration convection near Poyang Lake in daytime of warm season

Poyang Lake (PL), the biggest freshwater lake in China, is situated in the East Asian Monsoon region, and has an important impact on local convection. In general, PL can result in convection in local region when it is a heat source in nighttime of warm season. However, at around noon on 4 May 2020 (PL is a cold source), a convection was triggered about 20 km west of PL, and rapidly enhanced and resulted in lightning when approaching PL, and then quickly weakened and disappeared after entering the main body of PL. In order to explore the convection formation, several observational data and the Weather Research and Forecasting model were applied in this study. Results show that when the convection approaches PL, its rapid enhancement is induced by PL, and after entering the main body of PL, its quick weakening is also resulted from PL. However, the initiation of the convection is mainly induced by the local topography west of PL under a favorable large-scale background. Mechanism analysis indicates that the strong low-level convergence near the west shore of PL associated with lake-land breeze is responsible for the rapid enhancement of the convection, and the low-level divergence over the main body of PL associated with the lake-land breeze and the increase of the low-level stability induced by cooling of PL jointly result in the quick weakening of the convection. The prevailing southerly wind in low level passes through the local topography (Meiling Mountain) west of PL, and is divided into southwesterly wind (flow around Meiling) and southerly wind (flow over Meiling), and they converge in the north of Meiling, triggering the convection. This study is not only important to deepen the understanding of PL affecting regional weather, but also helpful for improving the refined forecasting of convection near PL.

Comparison of Urban Canopy Schemes and Surface Layer Schemes in the Simulation of a Heatwave in the Xiongan New Area

Due to rapid growth and expansion, Xiongan New Area is at risk for heatwaves in the present and future induced by the urban heat island effect. Based on eight combined schemes, including two common WRF surface layer schemes (MM5 and Eta) and urban canopy schemes (SLAB, UCM, BEP and BEP + BEM), simulation performance for 2-m temperature, 2-m relative humidity and 10-m wind during a heatwave in July 2019 was compared and analyzed. The simulation performance is ranked from best to worst: 2-m temperature, 2-m relative humidity, 10-m wind direction and 10-m wind speed. MM5 simulate 2-m temperature and 10-m wind speed better than Eta, but 2-m relative humidity worse. MM5 coupling BEP + BEM provides the highest simulation performance for 2-m air temperature, 10-m wind direction and 10-m wind speed but the worst for 2-m relative humidity. MM5 and Eta produce nearly opposite results for wind direction and wind speed. Due to the Anxin station close to Baiyang Lake, lake-land breeze affects the simulation findings, worsening the correlation between simulated 10-m wind and observation.

Lake-land breezes over a small elongated lake (Kozjak, Plitvice Lakes, Croatia)

The temperature of a small elongated lake (2.3 km by 0.1-0.6 km; maximum depth of 46 m) located in a mountaneous area was measured during July-September period over three years (2018-2020) at the depth close to the lake surface (0.2 m). Concurrent standard meteorological variables were measured in the vicinity of the lake. Criteria based on atmospheric and lake conditions were defined to detect the days with persistent lake-land breeze (LLB) events. The results showed that 17.7% of the investigated days were associated with LLB events. These days were accompanied by elevated energy in the normalized wavelet spectra for the wind speed at period of 24 hours. Daytime onshore lake breezes were mainly channeled in the along-lake direction due to the surrounding topography. Accordingly, during the daytime, diurnal wind veering was distorted. However, during the nighttime, a clear clockwise wind rotation was present. In addition, the results exhibited a clear relationship between the lake-land temperature difference and the strength of the LLBs.

Investigating the climatology of North China's urban inland lake based on six years of observations

There are unclear characteristics of the effect of lake breeze in small urban inland lakes due to little research on lake breezes. In this work, six-year observations were performed to study the comprehensive climatologic characteristics of lake breezes on North China's urban inland lake, Lake Hengshui (75 km2). By removing background winds calculated by ERA5 data and successfully recording the lake-land breeze cycle, we devised a succinct and effective approach for distinguishing lake-land breezes. Lake-land breeze had a high annual occurrence frequency of 13.4%–24.7% and a yearly mean lake-breeze speed of 1.6 m/s and yearly mean lake-breeze duration of 4.8 h; spring has the highest frequency and summer has the lowest frequency because of the greater thermal differences between lake and land in spring. The lake breeze mostly started at 06:00–07:00 and 10:00–13:00 (LST), showing a double-peak pattern, and ended at 17:00–19:00 (LST). On the other hand, the land breezes mainly started at 00:00–01:00 (LST) and ended at 05:00–06:00. The distance between each station and the lake has a negative correlation to the frequency and duration of the lake-land breeze, showing the higher frequency and duration at the near stations and the lower frequency and duration at the stations far from the lake. The land breeze has similar spatial characteristics. Winter has relatively lower seasonal average wind speeds of the lake breeze at most stations; spring and winter have high average wind speeds of the land breeze at each station, while summer and autumn have low. The study of the city lake's lake-land breeze will shed new insights into addressing the urban layout.

Impact of Interaction between Metropolitan Area and Shallow Lake on Daily Extreme Precipitation over Eastern China

Both cities and lakes have significant impacts on regional precipitation. With global warming, extreme precipitation events in Eastern China have increased significantly, and the single/joint influences of metropolises and lakes on extreme precipitation still need to be quantitatively evaluated. To reveal the impact of the single/joint influences of metropolises and lakes on the shear line torrential rain process, the Suzhou-Wuxi-Changzhou Metropolitan Area (SXCMA) and Lake Taihu in Eastern China were selected as the study area. Utilizing a WRF model, comparative studies of sensitivity simulations were conducted for the two typical extreme precipitation events caused by the low-level shear line (LLSL) on 27 June 2015 (EP627) and 25 September 2017 (EP925). Both results show that the existence of Lake Taihu and SXCMA will increase precipitation in the study area. SXCMA has a more obvious effect on enhancing precipitation, which is about twice the effect of Lake Taihu. SXCMA mainly strengthens the intensity and movement of the surface convergence line (SCL) in the study area and indirectly affects the shift of the LLSL, which finally affects the intensity and location of precipitation. Lake Taihu affects the intensity and movement of SCL, triggering ground vertical convections due to lower surface roughness, and acts as a land-lake breeze and water vapor source, which will affect the distribution and intensity of precipitation.

Aircraft observations and sub‐km modelling of the lake–land breeze circulation over Lake Victoria

AbstractThe lake–land breeze circulation over Lake Victoria was observed in unprecedented detail with a research aircraft during the HyVic pilot flight campaign in January 2019. An evening and morning flight observed the lake and land breezes respectively under mostly dry conditions. The circulation was observed at various heights along a transect across the lake and onshore in Tanzania. Profiles of the lower troposphere were recorded by dropsondes over the lake and land. Convection‐permitting MetUM simulations with different horizontal grid‐spacings (including sub‐km) were run for the flight periods. During the evening flight, the aircraft crossed the lake breeze front over land at 1627 LT, approximately 50 km to the east of the lake shore, recording a 6 gkg decrease in specific humidity and reversal in wind direction over 5 km. During the morning flight, a shallow land breeze was observed across the eastern shore at 0545 LT. At least one region of increased and deeper moisture (previously seen in simulations but never observed) was sampled over the lake surface between 0527 and 0855 LT. This bulge of moisture was likely formed from the lifting of near‐surface moist air above the lake by low‐level convergence. The observations and model simulations suggest that low‐level convergence occurred at the leading edge of the land breeze, which had detached from the main land breeze and independently propagated westward across the lake with wave‐like characteristics. The MetUM simulations were able to reasonably reproduce the lake breeze front, bulge feature, and its propagation, which is a major achievement given the sparse observational data for model initialisation in this region. However, some timing, resolution and boundary‐layer depth biases require further investigation. Overall, this pilot campaign provided an unprecedented snapshot of the Lake Victoria lake–land breeze circulation and motivates a more comprehensive field campaign in the future.

Temporal dynamics and drivers of lake ecosystem metabolism using high resolution observations in a shallow, tropical, eutrophic lake (Laguna Lake, Philippines)

The physical, chemical, and biological dynamics under changing atmospheric conditions of Laguna Lake, Philippines were analyzed from intensive observations. Diel measurements were conducted for 48 continuous hours for both dry and wet tropical seasons in addition to fine resolution long-term monitoring. Results revealed significant vertical and diel variations of lake variables in spite of a shallow water depth (2.5 m) caused by the intense surface heating from solar irradiance (~800 W m−2) and accentuated by the lake's high turbidity (16–32 ftu). Late afternoon land-lake breeze (~5–7 m s−1) regularly breaks daytime thermal stratification, and convective cooling at night maintains isothermal condition until dawn of the next day. The stratified condition demonstrated a wind-driven, density-induced 2-layer current pattern with a windward moving epilimnion (~4 folds faster) and a compensating hypolimnetic flow in the general lake circulation direction. Laguna Lake was observed to have a dominating diel cycle but also undergoes significant seasonal limnological variations brought primarily by climate, hydrology, and its interaction with the adjacent sea. Significantly correlated variations of pH, chlorophyll-a and DO in the dry season were indicative of the higher biological activity associated with the intrusion of polluted waters from Metro Manila. The non-occurrence of thermal over-turn was observed to be regularly followed by bottom hypoxic conditions (2–4 mg L−1), indicative of the eutrophic condition of the lake and the importance of diel wind-induced mixing in the bottom supply of DO. Laguna Lake was found to be predominantly net heterotrophic (GPP:R < 1, NEP < 0).

The Effects of Lake Representation on the Regional Hydroclimate in the ECMWF Reanalyses

AbstractLakes are an integral part of the geosphere, but they are challenging to represent in Earth system models which either exclude lakes or prescribe properties without simulating lake dynamics. In ECMWF Interim reanalysis (ERA-Interim), lakes are represented by prescribing lake surface water temperatures (LSWT) from external data sources, while the newer generation ERA5 introduces the FLake parameterization scheme to the modelling system with different LSWT assimilation data sources. This study assesses the performance of these two reanalyses over three regions with the largest lakes in the world (Laurentian Great Lakes, African Great Lakes, and Lake Baikal) to understand the effects of their simulation differences on hydrometeorological variables. We find that differences in lake representation alter the associated hydrological and atmospheric processes and can affect regional hydroclimatic assessments. There are prominent differences in LSWT between the two datasets which influence the simulation of lake-effect snowstorms in the Laurentian winters and lake-land breeze circulation patterns in the African region. Generally, ERA5 has warmer LSWT in all three regions for most months (by 2-12 K) and its evaporation rates are up to twice the magnitudes in ERA-Interim. In the Laurentian lakes, ERA5 has strong biases in LSWT and evaporation magnitudes. Over Lake Baikal and the African Great Lakes, ERA5 LSWT magnitudes are closer to satellite-based datasets, albeit with warm bias (1-4 K), while ERA-Interim underestimates the magnitudes. ERA5 also simulates intense precipitation hotspots in lake proximity that are not visible in ERA-Interim and other observation-based datasets. Despite these limitations, ERA5 improves the simulation of lake-land circulation patterns across the African Great Lakes.

Lake-atmosphere exchange impacts ozone simulation around a large shallow lake with large cities

Weather Research and Forecast model coupled with Chemistry (WRF-Chem) coupled with CLM4.5 lake model is used to understand the impacts of lake-atmosphere exchange on ozone concentration in the Lake Taihu region during a high temperature and high ozone concentration event. About 8 °C bias in lake surface temperature simulated by different lake schemes significantly change the structure and evolution of the lake-land breeze system. As a result, the vertical and horizontal advection directly impacts distribution of ozone around and over the lake in early morning, the difference in ozone concentration is 20–60 μg m−3. Location of the lake breeze front and development of the thermal inner boundary layer around midday are also highly sensitive to the lake-atmosphere exchange. In addition, difference in the local circulation patterns leads to distinct spatial distributions of NOx, an ozone precursor, in regions downwind of their emission sources, especially along the Yangtze River. In response, ozone concentration in this region is drastically changed (about 80 μg m−3) due to the combined actions of transport and chemical reactions. Overall, this study highlights that in regions with spatially extensive shallow lakes with megacities, it is important to accurately represent the lake-atmosphere exchange for ozone pollution simulations, especially under high-temperature and light-wind conditions, in which ozone high concentration events occur frequently and effects of the local lake breeze are expected to dominate.

Analysis of a Convective Storm Crossing Poyang Lake in China

A convective storm crossing Poyang Lake (PL) in China during 1200-1600 UTC on 13 May 2015 is examined. The results show that this storm occurs ahead of a 500-hPa trough with weak low-level temperature advection and a convectively stable layer between 925 and 850 hPa, and the tail of the storm is enhanced when its spearhead sweeps over PL after the sunset. Due to the heating and moistening of PL, the convectively stable layer over PL is destabilized; and instead, a deep (below 700 hPa) convectively unstable layer is organized. Moreover, both the radiative cooling and the storm-induced cooling result in a rapid air (near-surface) and land temperature decrease in the surrounding areas. Thus, a large lake-land temperature difference (about 6°C) occurs, which is conducive to generating land-lake breeze and enhancing the convergence of the low-level wind. Finally, the PL-induced deep convectively unstable layer and the enhanced low-level convergence jointly strengthen the crossing storm. To further confirm this, two simulations (with or without PL) are conducted with the Weather Research and Forecast (WRF) model. The simulation with PL successfully reproduces the evolution of the storm crossing PL, while the simulation without PL fails. In the simulation with PL, a high θse tongue at 850 hPa associated with the storm moves eastward and downward, and merges with the PL-induced lake boundary layer, forming a deep convectively unstable layer under 700 hPa. However, in the simulation without PL, the stable layer constantly maintains under 900 hPa. In addition, the 900-hPa wind difference between the simulations with and without PL shows a land-lake breeze circulation that strengths the convergence of the low-level wind.

The local climate impact of an African city during clear‐sky conditions—Implications of the recent urbanization in Kampala (Uganda)

AbstractThis study aims at assessing and understanding the impact of recent urbanization on the (surface) urban heat island ((S)UHI) under clear‐sky conditions in a tropical African city using different sources of remotely sensed data sets together with an urban climate model (UCM). The observed SUHI during clear sky conditions is found to be about 4°C on average over the capital city of Kampala, Uganda. The UCM, consisting of TERRA_URB embedded in COSMO‐CLM, represents the SUHI well during night but overestimates it by about 3°C in the mean during day. Moreover, a systematic warm land surface temperature bias of about 4°C is identified by night. Improved urban input parameters—derived from Local Climate Zones following the World Urban Database and Access Portal Tool (WUDAPT) framework—lead to a more realistic representation of spatial land surface temperatures patterns. In addition, this parameterization of the UCM can properly represent atmospheric variables such as air temperature, specific and relative humidity, as observed by the automated weather stations. A model sensitivity study furthermore demonstrates that the stronger urban heat island induced by the recent urbanization of Kampala over the past 15 years strongly interacts with the lake–land breeze circulation. Stronger daytime convection over the hotter city leads to areas of convergence that amplify the afternoon lake breeze in the Southern parts of the metropolis. Overall, this study demonstrates that the city of Kampala has a tangible effect on the regional climate that needs to be considered when studying present and future climate impacts.

Identifying Key Controls on Storm Formation over the Lake Victoria Basin

Abstract The Lake Victoria region in East Africa is a hot spot for intense convective storms that are responsible for the deaths of thousands of fishermen each year. The processes responsible for the initiation, development, and propagation of the storms are poorly understood and forecast skill is limited. Key processes for the life cycle of two storms are investigated using Met Office Unified Model convection-permitting simulations with 1.5 km horizontal grid spacing. The two cases are analyzed alongside a simulation of a period with no storms to assess the roles of the lake–land breeze, downslope mountain winds, prevailing large-scale winds, and moisture availability. While seasonal changes in large-scale moisture availability play a key role in storm development, the lake–land-breeze circulation is a major control on the initiation location, timing, and propagation of convection. In the dry season, opposing offshore winds form a bulge of moist air above the lake surface overnight that extends from the surface to ~1.5 km and may trigger storms in high CAPE/low CIN environments. Such a feature has not been explicitly observed or modeled in previous literature. Storms over land on the preceding day are shown to alter the local atmospheric moisture and circulation to promote storm formation over the lake. The variety of initiation processes and differing characteristics of just two storms analyzed here show that the mean diurnal cycle over Lake Victoria alone is inadequate to fully understand storm formation. Knowledge of daily changes in local-scale moisture variability and circulations are keys for skillful forecasts over the lake.

Influences of Lake Malawi on the spatial and diurnal variability of local precipitation

Abstract. We investigate how the intensity and spatial distribution of precipitation vary around Lake Malawi on a diurnal timescale, which can be valuable information for water resource management in tropical south-eastern African nations. Using a state-of-the-art satellite product and regional atmospheric model, the well-defined diurnal cycle is detected around Lake Malawi with harmonic and principle component analyses: the precipitation is intense during midnight to morning over Lake Malawi and the precipitation peaks in the daytime over the surrounding area. This diurnal cycle in the precipitation around the lake is associated with the lake–land breeze circulation. Comparisons between the benchmark simulation and an idealized simulation in which Lake Malawi is removed reveal that the diurnal variations in precipitation are substantially amplified by the presence of Lake Malawi. This is most evident over the lake and surrounding coastal regions. Lake Malawi also enhances the lake–land breeze circulation; the nocturnal lakeward land breeze generates surface convergence effectively and precipitation intensifies over the lake. Conversely, the daytime landward lake breeze generates the intense divergence over the lake and precipitation is strongly depressed over the lake. The lake–land breeze and the background vapour enriched by Lake Malawi drive primarily a diurnal variation in the surface moisture flux divergence/convergence over the lake and surrounding area which contributes to the diurnal cycle of precipitation in this region.

Physicochemical gradients and water fluxes between Nyanza Gulf and main Lake Victoria, East Africa: Tracing dynamics of gulf-main lake interaction

Abstract Variability in physico-chemical water column structure along a gradient between Nyanza Gulf and Lake Victoria was characterized, and the exchange between the two basins estimated. Specific conductivity (SC) measurements between March 2005 and March 2006 identified three morphologically distinct zones, the inner-gulf, the connecting Rusinga Channel and the main lake basin. The relatively shallow, wide and river-influenced inner-gulf had higher turbidity and SC compared to the channel and the main lake. The deep, narrow and more wind-exposed mid-channel area was significantly cooler than the rest of the study areas. Observational data revealed “density-driven” underflow of the cooler channel water into the main lake and compensatory surface flow into the gulf as well as seasonal patterns of gulf-main lake exchange in relation to variation in tributary input. The wind field was dominated by a diurnal lake-land breeze which resulted in wind-driven diurnal reversal of water flow in and out of the gulf, where the constriction of flow within the channel induced strong currents. The exchange between the gulf and the main lake was estimated using a box model, with SC as a conservative tracer. A net annual residual water flow of 35 m3 s−1 occurred from the gulf into the main lake although during months with low tributary discharge the flow was towards the gulf. The daily flow in and out of the gulf resulted in relatively high exchange flux compared to residual flow across the Rusinga Channel leading to the development of the well-defined physicochemical gradient along the Rusinga Channel.

Evaporation variability of Nam Co Lake in the Tibetan Plateau and its role in recent rapid lake expansion

Previous studies have shown that the majority of the lakes in the Tibetan Plateau (TP) started to expand rapidly since the late 1990s. However, the causes are still not well known. For Nam Co, being a closed lake with no outflow, evaporation (EL) over the lake surface is the only way water may leave the lake. Therefore, quantifying EL is key for investigating the mechanism of lake expansion in the TP. EL can be quantified by Penman- and/or bulk-transfer-type models, requiring only net radiation, temperature, humidity and wind speed for inputs. However, interpolation of wind speed data may be laden with great uncertainty due to extremely sparse ground meteorological observations, the highly heterogeneous landscape and lake-land breeze effects. Here, evaporation of Nam Co Lake was investigated within the 1979–2012 period at a monthly time-scale using the complementary relationship lake evaporation (CRLE) model which does not require wind speed data. Validations by in-situ observations of E601B pan evaporation rates at the shore of Nam Co Lake as well as measured EL over an adjacent small lake using eddy covariance technique suggest that CRLE is capable of simulating EL well since it implicitly considers wind effects on evaporation via its vapor transfer coefficient. The multi-year average of annual evaporation of Nam Co Lake is 635 mm. From 1979 to 2012, annual evaporation of Nam Co Lake expressed a very slight decreasing trend. However, a more significant decrease in EL occurred during 1998–2008 at a rate of −12 mm yr−1. Based on water-level readings, this significant decrease in lake evaporation was found to be responsible for approximately 4% of the reported rapid water level increase and areal expansion of Nam Co Lake during the same period.

Analysis of the Phenomenon of Lake-Land Breeze in Poyang Lake Area

Using the 2006-2010 conventional observed wind data from De' an,Poyang,Hukou,Jinxian and Xingzi,the lake-land breeze in Poyang Lake area was analyzed. These five observation stations are located within about 50 km radius of the Poyang Lake,which are respectively in the west,east,north,south and northwest parts of the Lake. The results show that lake-land breeze in Poyang Lake region occurs through the whole year,although it varies seasonally. Averagely,the strength of the zonal lake-land breeze is larger than the strength of the meridional lake-land breeze,with the values of 0. 5 ~ 0. 7 m ·s-1and 0. 3 m ·s-1respectively.The transition of lake-land breeze in the west of Lake is about two hours earlier than that in the east of Poyang Lake,and the transition of lake-land breeze in the north of Poyang Lake is about five hours earlier than that in the south of Poyang Lake. Analyses of the wind and temperature data in August 2010 from the 153 automatic meteorological stations in the Poyang Lake region show that the lake-land breeze presents diurnal variation obviously due to the lake-land temperature difference. The shallow wave model is employed to study the cause of the lake-land breeze in Poyang Lake region by setting the heating term as the Poyang Lake,and the model can simulate the land breeze during the night and lake breeze during daytime.

The Development of a Customization Framework for the WRF Model over the Lake Victoria Basin, Eastern Africa on Seasonal Timescales

Lake Victoria, Africa, supports millions of people. To produce reliable climate projections, it is desirable to successfully model the rainfall over the lake accurately. An initial step is taken here with customization of the Weather, Research, and Forecast (WRF) model. Of particular interest is an asymmetrical rainfall pattern across the lake basin, due to a diurnal land-lake breeze. The main aim is to present a customization framework for use over the lake. This framework is developed by conducting several series of model runs to investigate aspects of the customization. The runs are analyzed using Tropical Rainfall Measuring Mission rainfall data and Climatic Research Unit temperature data. The study shows that the choice of parameters and lake surface temperature initialization can significantly alter the results. Also, the optimal physics combinations for the climatology may not necessarily be suitable for all circumstances, such as extreme years. The study concludes that WRF is unable to reproduce the pattern across the lake. The temperature of the lake is too cold and this prevents the diurnal land-lake breeze reversal. Overall, this study highlights the importance of customizing a model to the region of research and presents a framework through which this may be achieved.

Eddy covariance measurements of water vapor and CO2 fluxes above the Erhai Lake

Measurement of turbulence fluxes were performed over the Erhai Lake using eddy covariance (EC) method. Basic physical parameters in the lake-air interaction processes, such as surface albedo of the lake, aerodynamic roughness length, bulk transfer coefficients, etc., were investigated using the EC data in 2012. The characteristics of turbulence fluxes over the lake including momentum flux, sensible heat flux, latent heat flux, and CO2 flux, and their controlling factors were analyzed. The total annual evaporation of the lake was also estimated based on the artificial neural network (ANN) gap-filling technique. Results showed that the total annual evaporation in 2012 was 1165 ± 15 mm, which was larger than the annual precipitation (818 mm). Local circulation between the lake and the surrounding land was found to be significant throughout the year due to the land-lake breeze or the mountain-valley breeze in this area. The prevailing winds of southeasterly and northwesterly were observed throughout the year. The sensible heat flux over this plateau lake usually had a few tens of W m−2, and generally became negative in the afternoon, indicating that heat was transferred from the lake to the atmosphere. The sensible heat flux was governed by the lake-air temperature difference and had its maximum in the early morning. The diurnal variation of the latent heat flux was controlled by vapor pressure deficit with a peak in the afternoon. The latent heat flux was dominant in the partition of available energy in daytime over this lake. The lake acted as a weak CO2 source to the atmosphere except for the midday of summer. Seasonal variations of surface albedo over the lake were related to the solar elevation angle and opacity of the water. Furthermore, compared with the observation data, the surface albedo estimated by CLM4-LISSS model was underestimated in winter and overestimated in summer.

Analysis of the microclimate and CO2 flux characteristics in arid desert wetland ecosystem in summer: A case study in Xihu desert wetland, Dunhuang, China

Xihu desert wetland is an important and unusual environment in China or even in the world. However, until now, little research has been focused on the microclimate and CO2 flux characteristics in this area. This paper reports the characteristics of daily variations of microclimate and CO2 flux in the Dunhuang Xihu desert wetland, based on data observed in the desert wetland during a period of continuous fine weather in summer 2012. Results indicate that the characteristics of the micrometeorology were significantly affected by the land–lake breeze during the study period, and updrafts were prevalent in this region. The friction wind speed and the vertical velocity were much greater than those in the Maqu grasslands. The energy budget was strongly imbalanced: the latent heat flux was significantly higher than the sensible flux. The daily mean values of total solar radiation and net radiation were larger than those in Maqu grasslands and Jinta oasis. There was a temperature inversion and inverse humidity gradient in the atmospheric surface layer at night. The desert wetland ecosystem was a carbon sink during the whole of the observation period, and the maximum rate of carbon absorption usually occurred at about 11:00 hr each day in this region.