Role Of Evapotranspiration Research Articles

Assessing the impact of evapotranspiration from green roofs on reducing surface temperatures

Evapotranspiration is an important process in green roofs to reduce surface temperature; however, it is still not well understood. This study aims to assess the influence of irrigation and vegetation parameters in the evapotranspiration of green roofs and surface temperature. Green roofs with almost no vegetation, short Sedum and tall Sedum with 0, 3 and 6 mm irrigation were considered in Lisbon (Portugal) and Florianópolis (Brazil) climates. The outside roof surface temperature was experimentally assessed in an extensive green roof prototype and used to validate the computer simulation. The results showed that although irrigation can enhance evapotranspiration, mainly in drier regions, denser vegetation has a higher impact on this process. The annual latent heat losses of the tall Sedum green roof overcome those of roofs with almost no vegetation by 695.9 kWh/m2 in Lisbon and by 471.8 kWh/m2 in Florianópolis. Green roofs with tall Sedum also resulted in lower substrate temperatures, even without irrigation. The hourly substrate temperature of green roofs with tall Sedum can be lower than the outside surface temperature of traditional roofs by up to 33.4 °C in Lisbon and up to 24.0 °C in Florianópolis. In these roofs, the latent heat fluxes correspond to 40 % and 48 % of the total losses in Lisbon and Florianópolis, respectively. It was concluded that latent heat losses accounted for a higher percentage of the energy balance of the green roofs whose reductions in surface temperature were more significant. This research provides valuable insights regarding the relationship between evapotranspiration and surface temperature and the role of evapotranspiration on the energy balance of green roofs with crassulacean acid metabolism (CAM) plants.

Energy Surplus and an Atmosphere‐Land‐Surface “Tug of War” Control Future Evapotranspiration

AbstractThe 21st century evapotranspiration (ET) trends over the continental U.S. are assessed using innovative, energy‐based principles. Annual ET is projected to increase with high confidence at the rate of 20 mm for every 1℃ of rise in near‐surface air temperature, or 0.45 or 0.98 mm/year/year, depending on the emission scenario. The ET trajectory is dominated (58%) by the increase of land‐surface net radiative energy. An enhancement of the fraction of energy taken up by ET becomes a more important controller (53%) in late 21st century, under the high emission scenario. This increase is explained by the “tug of war” between atmospheric vapor demand and land‐surface ability to supply water. An assessment of future water availability (precipitation minus ET) shows no significant changes at the continental scale. This outcome nevertheless hides strong spatial variability, emphasizing the role of ET in shaping the distribution of water availability among human populations.

The role of continental evapotranspiration on water vapour isotopic variability in the troposphere

ABSTRACT Rainforests play an important role in hydrological and carbon cycles, both at regional and global scales. They pump large quantities of moisture from the soil to the atmosphere and are major rainfall hotspots of the world. Satellite-observed stable water isotope ratios have played an essential role in determining sources of moisture in the atmosphere. Satellites provide information about the processes involving vapour transport in different zones of the world, identifying sources of rainfall and distinguishing moisture transport in monsoonal systems. This paper focuses on major rainforests of the world (Southern Amazon, Congo and Northeast India) to understand the role of continental evapotranspiration in influencing tropospheric water vapour. We have used satellite measurements of 1H2H16O/1H2 16O from Atmospheric InfraRed Sounder (AIRS), evapotranspiration (ET), solar-induced fluorescence (SIF), precipitation (P), atmospheric reanalysis-derived moisture flux convergence (MFC) and wind to discern the role of ET in influencing water vapour isotopes. A global map of the correlation between δ 2Hv and ET-P flux indicates that densely vegetated regions in the tropics show the highest positive correlation (r > 0.5). Using mixing models and observations of specific humidity and isotopic ratio over these forested regions, we discern the source of moisture in pre-wet and wet seasons.

Tradeoffs in forest resilience to satellite-based estimates of water and productivity losses

Climate change is expected to intensify the global hydrological cycle via increased evapotranspiration (ET). Changes in ET have important consequences for water-related ecosystem services as well as for forest productivity. Forests play a critical role in ET: active trees sequester carbon at the expense of losing water, yet if they are not active, water remains in the trees, but productivity stalls. We estimated the capacity of forests to recover (resilience) from extreme water or productivity losses based on modeled ET through remote sensing methods across the conterminous USA. Results show there is a spatial tradeoff in resilience to water or productivity losses. Forests were more resilient to water loss in the drier west, and more resilient to productivity loss in the wetter east. Still, resilience was highly heterogeneous across the continent. Projections under climate change indicate both declines and increases of up to 13% in forest resilience, with broad regional trends but high spatial heterogeneity within regions. This study brings crucial satellite-based insights on how water dynamics, and consequentially productivity and water provision in forests, might be impacted by climate change.

Urbanization altered atmospheric humidity diurnally and seasonally through ecohydrological processes in five urban agglomerations in China

The large-scale conversion of vegetated land to urban use leads to a significant reduction in evapotranspiration (ET) due to the lack of vegetation, which may aggravate urban dry island (UDI) effect. Analysis of diurnal and seasonal (e.g. growing season) variations in UDI can help us to better identify the role of ET in processes of UDI. We compared six-hourly weather observation data (1980–2017) from 140 paired urban-rural stations across a large climatic gradient in China to explore how near-surface atmospheric dryness changed both diurnally and seasonally, and its relationship with urbanization-associated ecohydrological processes. We showed that the difference in atmospheric dryness (i.e. UDI intensity) between urban and rural areas, as measured by specific humidity (Δq < 0), is more pronounced during the daytime and growing seasons. The nighttime urban wet island (UWI, Δq > 0) effect partially offset daily UDI effect, which has made the latter underestimated. Intensified nighttime urban heat island (UHI) reduced the diurnal temperature range (DTR) in cities and thus enhanced nighttime UWI effect from 2000 to 2010. However, after 2010, nighttime UWI effect weakened or disappeared, whereas nighttime UDI intensified in humid cities, resulting in a significant increase in daily UDI. Intensified UHI and UDI are often closely coupled (synchronous occurrence) through latent heat (LE) or ET processes, especially after 2010. Our results indicate that the conversion of vegetated lands to urban impervious surface, especially in humid regions, leads to the reduction in transportation during daytime and evaporation at night in urban cores, which alters the relationships between near-surface air temperature, atmospheric moisture, and ET. The present diurnal and seasonal variations in UDI were delineated in detail to explicate the patterns and interconnections of local urban climate and surface ecohydrological processes, which are critical for ecosystem services in urban landscape design.

Environmental factors driving evapotranspiration over a grassland in a transitional climate zone in China

AbstractThe surface evapotranspiration (ET) process is the key link in the interaction between land and atmosphere. However, the influence of different environmental factors on ET over transitional climate zones and the physical pattern of the interaction between multiple factors remain unclear. Therefore, based on the continuous observation data during the vegetation growing season of a typical grassland in the Semi‐Arid Climate and Environment Observation of Lanzhou University (SACOL) station from 2007 to 2012, the influence pattern of multiple environmental factors on ET over China's transitional climate zone was analysed. Each environmental factor exhibited significant seasonal and interannual variations. The mean value of ET was 1.67 mm day−1. Although the maximum values of sensible heat flux and vapour pressure deficit occurred in April and June, respectively, the maximum values of other environmental factors appeared from July to August. Net radiation, soil moisture, and normalized difference vegetation index (NDVI) were the main controlling factors of ET over the grassland, with correlation coefficients of 0.54, 0.52, and 0.46, respectively. The analysis of multiple environmental factors showed that when soil moisture, wind speed, net radiation, and NDVI reached 0.2 m3 m−3, 2 m s−1, 100 W m−2, and 0.2, respectively, ET varied in contrast with vapour pressure, vapour pressure deficit, and air temperature under the influences of weather processes, land–atmosphere coupling, and drought stress. These findings deepen our understanding of the role of ET in the land–atmosphere coupling process over the transitional climate zone in China.

Spatiotemporal variations in evapotranspiration and its influencing factors in the semiarid Hailar river basin, Northern China

Evapotranspiration (ET) is a critical variable in the world's water cycle, and plays a significant role in estimating the impact of environmental change on the regional hydrothermal cycle. Moreover, as an essential of eco-hydrological processes, changes in ET may exceptionally impact the local climate and provide indicative information on the eco-system's functioning. The Hailar River Basin (HRB), located in northern China, is one of the most sensitive areas to climate warming. Under the influence of climate change in recent years, the vegetation dynamics of the basin have been significant and have had profound effects on the regional water cycle conditions and hydrological processes. The HRB is located in a semiarid region and ET is the main mode of water consumption. The ET response to climate change and vegetation dynamics is the focus of research on ecohydrological processes in this basin. In this study, a distributed hydrological model, the BTOPMC model, is used to evaluate the actual ET in the HRB from 1981 to 2020, based on in situ meteorological data as well as LAI data obtained by satellite remote sensing. The seasonal, interannual and spatial dynamics of ET were characterized. The contribution of meteorological factors to ET was calculated by sensitivity analysis and multiple linear regression analysis, and the predominant elements influencing the difference in ET in the HRB were also discussed. The results show that: (1) estimated ET values can clarify over 85% of the seasonal variation in the observed values (R2= 0.79, P < 0.001; R2= 0.84, P < 0.001), which demonstrates that the model has a high precision. (2) Over the past 40 years, the annual ET has shown a clear increasing trend and a large spatial heterogeneity in its spatial distribution, which is consistent with the trend of vegetation. It mainly shows that the eastern forest area is larger than the central forest–grass transition area and the western meadow steppe area. (3) Sensitivity and influential factor contribution analyses show that the main factor driving interannual variability in ET is climate warming, followed by precipitation. At the same time, vegetation dynamics also play a crucial role in ET, especially in areas with different vegetation types and high coverage, while climatic factors also have a strong influence on ET indirectly through vegetation. Due to its special geographic location, the HRB is more sensitive to global climate change and is a typical ecologically fragile area. Therefore, this study has important scientific value and social significance for maintaining ecological security and the sustainable use of water resources.

Estimation of evapotranspiration and its relationship with environmental factors in Jinghe River Basin

The Jinghe River Basin is an important grain-producing area in northwest China; yet, serious soil erosion and water shortage problems have greatly limited the development of agriculture in the region. Evapotranspiration (ET) is a key component of rational water resources planning and water cycle mechanism exploration; yet, studies in this region have mainly focused on rainfall and runoff sand transport, neglecting the role of ET. Therefore, to understand the characteristics of ET in the Jinghe River basin, we estimated the ET during the vegetation growing season (April to October) in 2018 using the surface energy balance system (SEBS) based on remote sensing images and meteorological data, and analyzed the characteristics of its spatio-temporal distribution and its relationship with environmental factors. The results showed that (1) SEBS has good applicability in the study area, with R1 between 0.57 and 0.77, RMSE between 0.98 and 1.15 mm / d, and MRE between 24% and 36% as verified with the lysimeter and ET products; (2) on the basin scale, the average daily ET showed a unimodal distribution with time, with variations ranging from 1.6 to 4.1 mm while spatially it showed that the mountainous forest and river catchment areas were overall higher than the loess plateau and hilly gully areas; (3) on the landscape scale, the vegetation with the highest average daily ET was broad-leaved forest, and the lowest was grassland. The vegetation with the highest ecological water demand was cultivated vegetation, and the lowest was meadow; (4) correlation analysis showed that rainfall, temperature, sunshine hours, and vegetation cover were positively correlated with ET. Among them, rainfall and temperature have the strongest correlation with ET and maybe the main factors affecting ET in the Jinghe River Basin.

Urbanization Impacts on Evapotranspiration Across Various Spatio‐Temporal Scales

AbstractUrbanization has been shown to locally increase the nighttime temperatures creating urban heat islands, which partly arise due to evapotranspiration (ET) reduction. It is unclear how the direction and magnitude of the change in local ET due to urbanization varies globally across different climatic regimes. This knowledge gap is critical, both for the key role of ET in the energy and water balance accounting for the majority of local precipitation, and for reducing the urban heat island effect. We explore and assess the impacts of urbanization on monthly and mean annual ET across a range of landscapes from local to global spatial scales. Remotely sensed land cover and ET available at 1 km resolution are used to quantify the differences in ET between urban and surrounding non‐urban areas across the globe. The observed patterns show that the statistically significant difference between urban and non‐urban ET can be estimated to first order as a function of local hydroclimate, with arid regions seeing increased ET, and humid regions showing decreased ET. Cities under cold climates also evaporate more than their non‐urban surroundings during the winter, as the urban micro‐climate has increased energy availability resulting from human activities. Increased ET in arid cities arises from municipal water withdrawals and increased irrigation during drought conditions. These results can help inform planners to improve the integration of environmental conditions into the design and management of urban landscapes.

Assessing Freshwater Changes over Southern and Central Africa (2002–2017)

In large freshwater river basins across the globe, the composite influences of large-scale climatic processes and human activities (e.g., deforestation) on hydrological processes have been studied. However, the knowledge of these processes in this era of the Anthropocene in the understudied hydrologically pristine South Central African (SCA) region is limited. This study employs satellite observations of evapotranspiration (ET), precipitation and freshwater between 2002 and 2017 to explore the hydrological patterns of this region, which play a crucial role in global climatology. Multivariate methods, including the rotated principal component analysis (rPCA) were used to assess the relationship of terrestrial water storage (TWS) in response to climatic units (precipitation and ET). The use of the rPCA technique in assessing changes in TWS is warranted to provide more information on hydrological changes that are usually obscured by other dominant naturally-driven fluxes. Results show a low trend in vegetation transpiration due to deforestation around the Congo basin. Overall, the Congo (r2 = 76%) and Orange (r2 = 72%) River basins maintained an above-average consistency between precipitation and TWS throughout the study region and period. Consistent loss in freshwater is observed in the Zambezi (−9.9 ± 2.6 mm/year) and Okavango (−9.1 ± 2.5 mm/year) basins from 2002 to 2008. The Limpopo River basin is observed to have a 6% below average reduction in rainfall rates which contributed to its consistent loss in freshwater (−4.6 ± 3.2 mm/year) from 2006 to 2012.Using multi-linear regression and correlation analysis we show that ET contributes to the variability and distribution of TWS in the region. The relationship of ET with TWS (r = 0.5) and rainfall (r = 0.8) over SCA provides insight into the role of ET in regulating fluxes and the mechanisms that drive precipitation in the region. The moderate ET–TWS relationship also shows the effect of climate and anthropogenic influence in their interactions.

Contribution of soil moisture variations to high temperatures over different climatic regimes

The coupling of soil moisture to climatic variables highly depends on soil moisture variability. Therefore, the activities affecting the soil moisture availability and dynamics such as land use/cover change and agricultural practices influence land-atmosphere interactions. Using soil moisture proxies, modeling studies have proven significant coupling of soil water variations to near-surface atmospheric temperature in some regions. However, these works have mostly applied the precipitation-based indices at a specific time scale. In the present study, the concurrent and lagged associations of the soil wetness variations and the high temperature index (HTI) across different climates in Iran were evaluated using Spearman’s rank test. Standardized precipitation index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) calculated at one-month and six-month scales were employed as soil moisture surrogates. When seasonal aridity index (AI) range was from 0.2 to 1.0 (transitional condition), SPEI1 and SPI1 were correlated significantly (p < 0.05) with HTI at 83.0 and 42.4 % of cases, respectively. However, when AI was below 0.2 (water-limited condition) or over 2.0 (energy-limited condition), the topsoil moisture indices showed an insignificant association with HTI at the majority of cases. A significant negative association existed between SPEI6 and HTI at most dry cases in which soil surface is dry but subsoil appears not to be fully depleted. Therefore, the topsoil and subsoil moisture variations are likely to affect high temperature occurrence under transitional and dry conditions, respectively. The insignificant lagged correlations found for most areas indicate poor linear relationship between high temperature occurrence and soil water dynamics in the preceding month over the study area. Furthermore, when AI exceed 0.2, ENSO-related soil drought is likely to cause a stronger soil moisture-temperature coupling. Overall, the role of evapotranspiration and soil moisture depth should be considered for assessing soil moisture dynamics and land-atmosphere interactions. Our findings may be helpful for adopting soil moisture-based adaptive measures to negate the impacts of high temperatures on agricultural products.

Evapotranspiration and biogeochemical regulation in a mountain peatland: insights from eddy covariance and ionic balance measurements

Study RegionThe mountainous catchments in the Australian Alps are one of the highest water-yielding regions within a generally dry continent. Peatlands are critical water-regulating components of these catchments, and their response to a changing climate will impact all downstream environments and water availability for human uses. Study FocusMountain peatland ecohydrology, and in particular the role of evapotranspiration, remains incompletely understood. This study focused on evapotranspiration and biogeochemical regulation of “Alpine Sphagnum Bogs”, with a case study at Watchbed Creek peatland. Eddy covariance was used to quantify evapotranspiration and combined with Penman-Monteith-based evapotranspiration to calculate an ‘ecosystem vegetation coefficient’ (KESV). Base-flow evapotranspiration and analyses of Cl−, Na+, Ca2+ and Mg2+ in peatland stream water were used to assess biogeochemical processes. New Hydrological Insights for the RegionThis work demonstrates that evapotranspiration is a major component of the water budget, 26% of annual precipitation. Further, we show how KESV calculated from direct measurements at one site may enable evapotranspiration to be modelled for other mountain catchments. The seasonally dependent nature of the biogeochemical regulation processes observed in this mountain peatland can be used as a reference to evaluate the condition of peatlands under similar synoptic weather conditions. In practice, this means that mountain ecosystem restoration can now be informed by a better understanding of the ecohydrology of these critical high mountain catchments.

Land Development and Role of Evapotranspiration in Climate Change

Analyses of underground temperatures have been used to obtain ground surface temperature (GST) histories. At individual sites, changes in the GST over time are synchronous with development which altered the evapotranspiration. At different, closely spaced sites, measured differences in GST between sites depend on the relative amounts of evaporation and transpiration at each site. These observations prove that a significant portion of the climate change observed on land is caused by changes in the amounts of evapotranspiration at each location. The magnitudes of GST changes vary from 0.6 to 2.6 C, for developments occurring from 8 to 52 years ago. In the temperate zone of Canada, these differences occur primarily in the summer. Our development, including urbanization and development of agricultural land, has produced a significant warming. It is best defined from underground temperature data.

Performance Analysis of Daily Global Solar Radiation Models in Peru by Regression Analysis

Solar radiation (Rs) is one of the main parameters controlling the energy balance at the Earth’s surface and plays a major role in evapotranspiration and plant growth, snow melting, and environmental studies. This work aimed at evaluating the performance of seven empirical models in estimating daily solar radiation over 1990–2004 (calibration) and 2004–2010 (validation) at 13 Peruvian meteorological stations. With the same variables used in empirical models (temperature) as well as two other parameters, namely precipitation and relative humidity, new models were developed by multiple linear regression analysis (proposed models). In calibration of empirical models with the same variables, the lowest estimation errors were 227.1 and 236.3 J·cm−2·day−1 at Tacna and Puno stations, and the highest errors were 3958.4 and 3005.7 at San Ramon and Junin stations, respectively. The poorest-performing empirical models greatly overestimated Rs at most stations. The best performance of a proposed model (in terms of percentage of error reduction) was 73% compared to the average of all empirical models and 93% relative to the poorest result of empirical models, both at San Ramon station. According to root mean square errors (RMSEs) of proposed models, the worst and the best results are achieved at San Martin station (RMSE = 508.8 J·cm−2·day−1) and Tacna station (RMSE = 223.2 J·cm−2·day−1), respectively.

Vegetation‐groundwater dynamics at a former uranium mill site following invasion of a biocontrol agent: A time series analysis of Landsat normalized difference vegetation index data

AbstractBecause groundwater recharge in dry regions is generally low, arid and semiarid environments have been considered well‐suited for long‐term isolation of hazardous materials (e.g., radioactive waste). In these dry regions, water lost (transpired) by plants and evaporated from the soil surface, collectively termed evapotranspiration (ET), is usually the primary discharge component in the water balance. Therefore, vegetation can potentially affect groundwater flow and contaminant transport at waste disposal sites. We studied vegetation health and ET dynamics at a Uranium Mill Tailings Radiation Control Act (UMTRCA) disposal site in Shiprock, New Mexico, where a floodplain alluvial aquifer was contaminated by mill effluent. Vegetation on the floodplain was predominantly deep‐rooted, non‐native tamarisk shrubs (Tamarix sp.). After the introduction of the tamarisk beetle (Diorhabda sp.) as a biocontrol agent, the health of the invasive tamarisk on the Shiprock floodplain declined. We used Landsat normalized difference vegetation index (NDVI) data to measure greenness and a remote sensing algorithm to estimate landscape‐scale ET along the floodplain of the UMTRCA site in Shiprock prior to (2000–2009) and after (2010–2018) beetle establishment. Using groundwater level data collected from 2011 to 2014, we also assessed the role of ET in explaining seasonal variations in depth to water of the floodplain. Growing season scaled NDVI decreased 30% (p &lt; .001), while ET decreased 26% from the pre‐ to post‐beetle period and seasonal ET estimates were significantly correlated with groundwater levels from 2011 to 2014 (r2 = .71; p = .009). Tamarisk greenness (a proxy for health) was significantly affected by Diorhabda but has partially recovered since 2012. Despite this, increased ET demand in the summer/fall period might reduce contaminant transport to the San Juan River during this period.

El papel de la evapotranspiración en la distribución funcional foliar de 28 especies del género Quercus de España y México

de la Riva, E.G., Arenas, M., Villar, R., Garcia-Oliva, F., Oyama, K. 2019. The role of evapotranspiration on the foliar functional distribution of 28 Quercus species from Mexico and Spain. Ecosistemas 28(3):199-207. Doi.: 10.7818/ECOS.1803 Quercus species represent the most important woody genus in the northern hemisphere, with broad environmental distribution in Spain and Mexico. Functional plant traits are commonly used as indicators of species diversification and environmental adaptations, and they allow us to better understand the morphological and physiological limitations of the species that restrict its evolution. The main objective of this study is to explore the spectrum of variation of Quercus genus, by analyzing the variation in five functional leaf traits of 28 Quercus species from Spain and Mexico along an environmental gradient of potential evapotranspiration. We found two major dimensions of functional variation: on one hand, the species are segregating along the humidity gradient according with the leaf economics spectrum. Therefore, we found species associated to a conservative use of resources in areas with higher evapotranspiration rate and acquisitive species in the areas with lower evapotranspiration. On the other hand, the leaf size is mainly determined by the geographical origin of the species. These results suggest that the evolutionary modifications within the same genus are related with the leaf traits variation, being humidity a key factor of functional trait variation within the Quercus genus. In addition, we would like to highlight that we do not find relationship between leaf longevity and leaf economic spectrum, which may be explained by the different evolutionary histories of the leaf habit in oaks between both countries.

Effects of Soil Properties and Illumination Intensities on Matric Suction of Vegetated Soil

Matric suction induced by evapotranspiration is an important parameter for determining the hydraulic mechanisms of vegetation on slope stability. Despite evapotranspiration closely associated with atmospheric parameters and soil conditions, the influence of soil properties and illumination intensities on matric suction of vegetated soil has so far received the least research attention. In this paper, three kinds of soil, namely, fine sandy loam, sandy silt, and silty clay, were selected as experimental soils, and Indigofera amblyantha was chosen as the test plant. The test conditions were controlled, such as the use of homogeneous soil and uniform plant growth conditions. Each specimen was exposed to identical atmospheric conditions controlled in a laboratory for monitoring matric suction responses over 10 days. The results showed that illumination intensities play an important role in evapotranspiration, and the thermal energy from lighting had a direct impact on plant transpiration, whereas the lighting only affected plant photosynthesis. Plant roots in vegetated soil can effectively improve the air intake value of soil, and matric suction induced by plant transpiration in vegetated soil was 1.5–2.0 times that of un-evapotranspirated soil. There is a correlation between matric suction and the silt and clay contents, and the matric suction of silty clay was sensitive to changes in the soil moisture content. Compared to fine sandy loam, the water retention of sandy silt and silty clay was high, and a high level of matric suction was maintained in the corresponding time. The results for predicting soil water evapotranspiration based on matric suction have theoretical and practical significance for preventing soil erosion and shallow landslides. In addition, these results have great guiding significance for agricultural production, such as irrigation.

Seasonal variation of evapotranspiration and its effect on the surface energy budget closure at a tropical forest over north-east India

This study uses 1 yr of eddy covariance (EC) flux observations to investigate seasonal variations in evapotranspiration (ET) and surface energy budget (SEB) closure at a tropical semi-deciduous forest located in north-east India. The annual cycle is divided into four seasons, namely, pre-monsoon, monsoon, post-monsoon and winter. The highest energy balance closure (76%) is observed during pre-monsoon, whereas the lowest level of closure (62%) is observed during winter. Intermediate closure of 68% and 72% is observed during the monsoon and post-monsoon seasons, respectively. Maximum latent heat flux during winter (\(\hbox {150 W m}^{-2}\)) is half of the maximum latent heat (\(\hbox {300 W m}^{-2}\)) flux during the monsoon. ET is a controlling factor of SEB closure, with the highest rates of closure corresponding to the periods of the highest ET. The Bowen ratio ranges from 0.93 in winter to 0.27 during the monsoon. This is the first time the role of ET in the seasonal variation of SEB closure has been reported for any ecosystem in north-east India using EC measurements.

The role of evapotranspiration in streamflow modeling – An analysis using entropy

Informational entropy can be used to elucidate some important relationships between precipitation, evapotranspiration (ET), and discharge over a range of spatial and temporal scales. Entropy does not suffer from any a priori assumptions of linearity or distributional characteristics. In a study of the Southeastern United States, entropy and mutual information were used to identify relationships between hydrologic variables over spatial scales from a few hundred to several thousand km2 and temporal scales from days to months. Two distinct ET data sets were compared- one based on a highly parameterized energy budget approach and the other based on a complex iterative solution and a modified Penman method. It was found that there was a considerable difference in uncertainty between the two methods and that, although they each contained some amount of explanatory information regarding streamflow the more complex approach contained the most shared information. Further, it was found that streamflow entropy, or uncertainty, increased with drainage area, indicating that larger basins have more uncertainty to be reduced, in that more information can possibly be gained through the knowledge of other variables. However, the knowledge of ET reduces a greater proportion of uncertainty in smaller basins (<1500 km2), while larger basins have more unexplained variability.

1845–2016 gridded dataset of monthly precipitation over the upper Adda river basin: a comparison with runoff series

Abstract. A new high-resolution gridded dataset of 1845–2016 monthly precipitation series for the upper Adda river basin was computed starting from a network of high-quality and homogenised station records covering Adda basin and neighbouring areas and spanning more than two centuries. The long-term signal was reconstructed by a procedure based on the anomaly method and consisting in the superimposition of two fields which were computed independently: 1961–1990 monthly climatologies and gridded anomalies. Model accuracy was evaluated by means of station series reconstruction in leave-one-out approach and monthly relative mean absolute errors were found to range between 14 % in summer and 24 % in winter. Except for the period before the 1870s when station coverage is rather low, reconstruction errors are quite stable. The 1845–2016 monthly areal precipitation series integrated over Adda basin was finally computed. The robustness of this series was evaluated and it was investigated for long-term trend. While no significant trend emerged for precipitation, the analysis performed on 1845–2016 annual runoff values recorded at Lake Como outlet highlighted a negative trend. Runoff decrease is supposed to be mostly due to an increasing role of evapotranspiration linked to temperature increase, which is only partially compensated by the increase in glacier melting rate. In order to test the applicability of the gridded database for the reconstruction of extreme past events, the episode with the highest precipitation in Adda basin series (November 2002) was considered and the corresponding gridded fields of monthly anomalies and precipitation values were evaluated both with actual station density and with station densities corresponding to 1922 and 1882. Even considering 1882 station density, the main spatial patterns are well depicted proving the suitability of anomaly method to deal also with sparse station networks.