Variables Potential Evapotranspiration Research Articles

Characteristics and determining factors of spring-summer consecutive drought variations in Northwest China

Northwest China (NWC, defined by its administrative division) is an arid and semi-arid region where continuous drought occurs in spring and summer that severely affects crop growth and yields. However, the characteristics of spring-summer consecutive drought (SSCD) in NWC remain unknown. Based on daily observation data from 118 stations in NWC for the period 1961–2017, we investigated the variations in SSCD, as defined by the standardized precipitation evapotranspiration index (SPEI), and their determining factors. The SSCD intensity in NWC underwent a two-stage change rather than a sustained non-significant decrease during 1961–2017. Specifically, this intensity significantly decreased before 1993 (−0.19 decade−1; p < 0.05) and increased thereafter (0.21 decade−1; p < 0.05). The variations in SSCD in NWC were primarily determined by the variations in potential evapotranspiration (ET0). The decrease and increase in ET0 (−19.52 mm decade−1 and 10.77 mm decade−1, respectively; p < 0.05) dominated those of SSCD in NWC during 1961–1993 and 1994–2017, respectively, with respective explanatory variances of 99.6% and 93.2%. Furthermore, the decrease in wind speed (−0.14 m s−1 decade−1; p < 0.05) dominated that in ET0 before 1993, whereas the decrease in relative humidity (−1.47% decade−1; p < 0.05) and the weak recovery of wind speed (−0.06 m s−1 decade−1; p < 0.05) jointly dominated the increase in ET0 after 1993. Along with the increased SSCD after 1993, significant changes also occurred in the atmospheric circulation. An intensified anticyclonic anomaly occurred to the west of NWC, which provided a favorable circulation background for the increase in SSCD in NWC after the early 1990s. These findings provide a basis for further understanding drought and sustainable agricultural development in NWC under climate change.

Effects of landscape attributes and climate variables on catchment hydrology

Catchments characteristics, such as geomorphology, geology, soil, land use, and climatic variables, play an important role in total stream flow responses, a critical resource for people and the environment. Most of the previous literatures were applied a conventional statistical regression model to assess the relationship between landscape-climate descriptors, and streamflow and PET. However, a conventional statistical regression model didn’t consider dependence of explanatory variables that were collected or extracted across both space and time. This paper investigated the impacts of landscape attributes and climate variables on catchment scale temporal variation of total streamflow and spatio-temporal variation of potential evapotranspiration (PET) in the Mille catchment using multiple linear regression techniques, and the importance of this study was to test spatial autocorrelation in the spatial regression model which is required to properly assess and quantify the relationship between hydrological regime response components and Landscape-climate descriptors in a catchment with topographically complex, and high spatio-temporal climatic variation like in our case study area, the Mille catchment. Statistical regression analysis revealed significant relationships between streamflow and climate variables, especially with rainfall. Mean maximum temperature is the most dominant factor controlling temporal variation of potential evapotranspiration at a monthly scale, whereas NDVI is the most significant factor that controls the spatial variability of PET. The multiple regression model shows that 91.1% of temporal variation in streamflow was accounted for rainfall, whereas, 96.6% and 78.4% of temporal and spatial variation in potential evapotranspiration was accounted for in maximum temperature and NDVI, respectively. Methods also can be applied to catchments with similar landscape attributes and climate variables.

Spatial distribution of the trends in potential evapotranspiration and its influencing climatic factors in Iraq

Understanding the spatial variations in potential evapotranspiration (PET) and its influencing climatic variables is essential for sustainable agriculture and water resources management. However, little published research has investigated the alternation of PET due to climate change in the case of Iraq. The objective of the present study was to analyze the spatial trends in annual and seasonal PET in Iraq. Accordingly, the latest global ERA5-Land dataset of the European Centre for Medium-Range Weather Forecasts for 1981–2021 was employed. The PET was estimated using the FAO-Penman–Monteith method. The modified Mann–Kendall statistical test was applied to evaluate the significance of the trends in PET, which can separate unidirectional trends caused by climate change from the natural variability of climate. The attained results indicate that: (1) Over the past four decades, the annual and seasonal PET witnessed a significant increasing trend in almost all of Iraq, except for the alluvial plain in the eastern and southeastern parts. (2) The increasing trend in PET confirmed the patterns of the trend significance, with the highest increase of 0.28–0.65 mm/decade in southwest Iraq. (3) Summer had the highest upward trend of 0.35–0.65 mm/decade, followed by spring, autumn, and winter. (4) The air temperature was the predominant driving factor of rising PET, showing a positive correlation ranging from 0.77 to 0.88 and a contribution of 26 to 94%, mainly in the south, central, and northwest regions. The reverse contribution of wind speed and surface pressure to PET, particularly in the southeast and southwest, remains offset by the influence of air temperature and net solar radiation. Overall, the PET has risen drastically due to global climate change, indicating the potential for increased atmospheric water demand in the region.

Climate change impacts on rainfed agriculture and mitigation strategies for sustainable agricultural management: A case study of Prince Edward Island, Canada

AbstractRainfed agriculture in Prince Edward Island is affected by climatic changes like warming, seasonal shifts, varying precipitations, and reducing water availabilities, all questioning its sustainability. Projecting future scenarios was critically important; therefore, spatiotemporal variations in potential evapotranspiration (PET), crop water requirements (CWRs), effective rainfall (ER), supplemental irrigation requirements (SIR), and sustainable water availabilities (SWAs) were analyzed. Average annual PET was predicted to insignificantly increase (3% to 6%) under RCP4.5 during the next 30–60 years, with two to four times increase in colder months (January–April) and a significant reduction during August–December. Accordingly, historical CWR of potatoes (currently ~425 mm) would decrease by 5% to 9%, except for the least likely RCP8.5 scenario, which projects ~10% increase in 2051–2080. That, and changes in ER, would cause SIR to decrease to 50–90 mm in normal years, but two to three times higher during dry years, and almost no SIR in wet years. Spatially, SIR increases by ~40 mm from east to west and is expected to be higher in 2021–2050 than 2051–2080. Monthly SIR ranges in normal years would be July: 02–36 mm, August: 31–48 mm, and September 04–20 mm. Existing water policy allows pumping up to 20% of yearly recharges (annual SWA) and up to 35% of summer's streams baseflows (summer SWA). Despite insignificant reductions in annual SWA (3% to 17%) for the next 30–60 years, summer SWA may be reduced 38% to 50% due to temporal redistribution. Even in dry years, the reduced amounts would still be sufficient to fulfill SIR in the eastern forest‐dominated Bear River watershed and SIR in normal years in the central zone; however, they would not be enough to enable the entire cultivated area of western zone. In normal years, SIR would consume: 5% to 6%, 27% to 37%, and 63% to 79% of annual SWA in the eastern, central, and western zones, respectively. Sprinkler irrigation to meet SIR is challenging, more economic evaluations and policy adaptations are needed for sustainable agricultural management.

Spatiotemporal variation of potential evapotranspiration and its dominant factors during 1970-2020 across the Sichuan-Chongqing region, China.

Analyzing the primary factors of potential evapotranspiration (PET) dynamic is fundamental to accurately estimating crop yield, evaluating environmental impacts, and understanding water and carbon cycles. Previous studies have focused on regionally average regional PET and its dominant factors. Spatial distributions of PET trends and their main causes have not been fully investigated. The Mann–Kendall test was used to determine the significance of long-term trends in PET and five meteorological factors (net radiation, wind speed, air temperature, vapor pressure deficit, relative humidity) at 56 meteorological stations in the Sichuan-Chongqing region from 1970 to 2020. Furthermore, this present study combining and quantitatively illustrated sensitivities and contributions of the meteorological factors to change in annual and seasonal PET. There was a positive trend in PET for approximately 58%, 68%, 38%, 73% and 73% of all surveyed stations at annual, spring, summer, autumn and winter, respectively. Contribution analysis exhibited that the driving factors for the PET variation varied spatially and seasonally. For stations with an upward PET trend, vapor pressure deficit was a dominant factor at all time scales. For stations with a downward PET trend, annual changes in PET mainly resulted from decreased wind speed, as did changes in spring, autumn and winter; decreasing net radiation was the dominant factor in summer. The positive effect of the vapor pressure deficit offset the negative effects of wind speed and net radiation, leading to the increasing PET in this area as a whole. Sensitivity analysis showed that net radiation and relative humidity were the two most sensitive variables for PET, followed by vapor pressure deficit in this study area. Results from the two mathematical approaches were not perfect match, because the change magnitude of the meteorological factors is also responsible for the effects of meteorological factors on PET variation to some extent. However, conducting sensitivity and contribution analysis in this study can avoid the uncertainties from using a single method and provides detailed and well-understood information for interpreting the influence of global climate change on the water cycle and improving local water management.

Changes of potential evapotranspiration and its sensitivity across China under future climate scenarios

Global warming can exacerbate changes in the hydrological cycle. Understanding future changes in potential evapotranspiration (PET) under global warming is highly significant to irrigation planning and water resource management. Here, we use the Mann-Kendall test and Sobol’ method to analyze the spatiotemporal variations in PET and identify factors controlling its changes for two climate change scenarios during 2021–2050. Sobol’ method describes the ability of individual variables to affect PET and describes the impact of the interaction between variables. Results show that the most sensitive meteorological variable in the Songhuajiang River basin, Yangtze River basin, Zhujiang River basin, Southeast river basins, and Southwest river basins is solar radiation (Ra). At the same time, it is the maximum temperature (Tmax) in the remaining basins. Under a high radiative forcing, PET is more sensitive to Ra. PET is greatly affected by the interactions between Ra and other meteorological variables in the basins located in the northern part of China. In contrast, it is the interactions between temperature and others in the remaining basins. In summer and autumn, PET is more sensitive to Ra than in spring and winter in northern China. Our findings can provide helpful information for the development and utilization of water resources in China.

Analysis of the variation in potential evapotranspiration and surface wet conditions in the Hancang River Basin, China

Evapotranspiration is an important component of the water cycle, and possible trends in evapotranspiration can, among others, influence water management and agricultural production. Potential evapotranspiration (ETp) is a measure of the ability of the atmosphere to remove water from the surface through the processes of evaporation and transpiration. It plays an important role in assessing regional dry–wet conditions and variations in meteorological conditions. This study analyzed the change trends of monthly ETp and surface dryness and wetness in the Hancang River Basin and, through principal component analysis and correlation analysis, explored the main meteorological factors that affected ETp and the interactions between meteorological factors; ETp values were estimated using the FAO-56 Penman–Monteith method. The results showed that there was a large gap in ETp between different months in the Hancang River Basin, with a trend of first increasing and then decreasing within a year. The highest monthly evapotranspiration was 114.119 mm (July), and the lowest was 42.761 mm (January). The maximum relative humidity index was 0.822 (August), and the minimum was -0.979 (January). The average temperature, precipitation, average relative humidity, and solar radiation are positive factors that affect ETp, while average air pressure is a negative factor that affects ETp. This study provides a reference for the wet conditions of small watersheds and for countermeasures to address climate change.

The sensitivity of the SPEI to potential evapotranspiration and precipitation at multiple timescales on the Huang-Huai-Hai Plain, China

The standardized precipitation evapotranspiration index (SPEI) is considered appropriate for drought assessment. In this study, changes in drought characteristics and the sensitivity of SPEI to variations in potential evapotranspiration (PET) and precipitation (P) were detected at different timescales (1, 3, 6, and 12 months) on the Huang-Huai-Hai Plain in China from 1901–2015. The results showed that obvious wetting trends were found in this plain and higher SPEI values that were mostly located in the north. Additionally, the SPEI values showed a wetting trend across 83.4%, 99.6%, 98.6%, and 86.6% of the plain at the 1-month (SPEI-01), 3-month (SPEI-03), 6-month (SPEI-06), and 12-month (SPEI-12) timescales, respectively. Obviously, the SPEI displayed a stronger correlation with P than the PET, which was primarily due to the complicated SPEI calculation process. These findings provide critical guidance for sustainable ecological development with the use of the SPEI to detect the impacts of climate factors on drought.

Potential evapotranspiration trends in West Africa from 1906 to 2015

In this study, Climate Research Unit monthly observations were used to assess the trends of potential evapotranspiration (PET) over West Africa from 1906 to 2015. Trends and changes in PET during the 110-year study period and two reference climatological periods (1931–1960 and 1961–1990) were examined. Nonparametric trend test of the Mann–Kendall and Kolmogorov–Smirnov was employed to find the changes in trends of PET and their significance or otherwise. The contributions of some meteorological parameters (air temperatures, precipitation and cloud cover) to the observed trends in PET were also examined. Results of long-term data analysis showed mixed trends in PET in the three designated zones (Guinea, Savanna and Sahel) but notable significant increasing trends (0.165 mm per year) at p = 0.1 in Sahel. However, very sharp differences in PET were observed in both reference periods across the zones with significant decreasing trends (at p = 0.01) in PET during the first period but increasing significant trends (at p = 0.1) during the second. In spite of this pattern of variations, general reductions in PET (− 0.6% to − 1.2%) were observed, which were found to be triggered by decrease in temperature (− 0.13 to − 1.07%) and vapour pressure (− 0.02 to − 0.33%) as well as increase in cloudiness (0.01–0.05%). However, the magnitudes of changes in PET were found to be insignificant in all the zones. Maximum temperature, more than other dominant climatic parameters, contributed significantly (Theil–Sen’s regression: 23.5% ≤ β ≤ 50.3%; p = 0.01) to observed variations in PET.

Trends of actual and potential evapotranspiration based on Bouchet’s complementary concept in a cold and arid steppe site of Northeastern Asia

Due to complex natural water flux processes and the ambiguous explanation of Bouchet’s complementary theory, site-level investigations on evapotranspiration (ET) and related climate variables assist in understanding the regional hydrological response to climate change. In this study, site specific empirical parameters were incorporated in the Bouchet’s complementary relationship (CR) and potential and actual ET were estimated by CR method and subsequently validated by 6 years of ground-based vapor flux observations. Time series analysis, correlation analysis and principal regression analysis were conducted to reveal the characteristics of climate change and the controlling factor(s) of the variations of potential ET and actual ET. The results show that this region is exhibiting a combined warming and drying trend over the past decades with two change points that occurred in 1993 and in 2000. Potential ET was predominantly influenced by temperature and vapor pressure deficit, while actual ET was mostly influenced by vegetation activity. Potential ET was found to be increasing concurrently with declining actual ET to constitute nearly a symmetric complementary relationship over the past decades. This study help to enhance our understanding of the regional hydrological response to climate change. Further studies are needed to partition the actual ET into transpiration and other components and to reveal the role of vegetation activity in determining regional ET as well as water balance.

Dynamics and Attributions of Baseflow in the Semiarid Loess Plateau

AbstractBaseflow is an all‐important replenishment feature of the hydrologic cycle for maintaining surface water in basins across the world. Understanding its dynamics and the influence of climate variability and human activities will be beneficial for developing sustainable water‐management strategies. In this study, we selected 11 basins within the Loess Plateau (a typical semiarid region in China) for assessment of the variations in baseflow and baseflow index (BFI; the ratio of baseflow volume to total streamflow volume) during the period 1961–2014. We compared eight baseflow separation methods and selected the median series in order to reduce the uncertainty. Results showed that values of the “Bflow” and Eckhardt filter methods were higher than values of the other six methods for the period of peak discharge. Annual baseflow exhibited a statistically significant downward trend (p &lt; 0.01) in all 11 basins except Qingjian and Yanhe basins, while nine basins trended upward for BFI. All basins exhibited downward trends for seasonal baseflow in all seasons, with Yanhe and Qingjian showing the least significant trend. Variations in both baseflow and the BFI were more sensitive to variations in potential evapotranspiration than to variations in precipitation. Across these 11 basins for both the conservation engineering period (1971–1999) and the reforestation period (2000–2014), human activities (73% and 76%, respectively) contributed more than climate variability (27% and 24%, respectively) to average baseflow decline. However, climate variability was the main factor altering the BFI, with the contribution accounting for about 54% and 76%, respectively, for the two periods.

Distribution of tree species with high economic and livelihood value for Zambia

The sustainable management of dry forests and woodlands of Sub-Saharan Africa (SSA) is crucial for the SSA economy and people’s livelihoods but it remains a key challenge to address. Maps of tree species distributions of economic value are lacking for the region; yet, this information is essential for supporting sustainable use. We capitalized on new nation-wide field survey data for the Republic of Zambia (Southern Africa) to generate the first suite of baseline species distribution models (SDMs) for 20 tree species of economic significance to support for sustainable management and conservation. We employed one regression- and two machine learning-based techniques to model and predict tree distribution. For each species, we compared the three model results for the relative importance of different predictive variables, revealing the most important predictors of each species niche and providing insight into how human activities influence current tree species distribution. Overall, environmental predictors that best explained tree species distribution were related to water availability, including mean potential evapotranspiration (PET), annual rainfall, and the variation in PET, as well as elevation and soil fertility. Human impact on distribution was notable for tree species used for charcoal and timber, including the proximity to roads for charcoal-favored species and the proximity to settlement for timber species. For all tree species, fire did not stand out as a variable of importance, contrary to expectations. The SDMs generated from this study will provide essential baseline information to support national conservation and management efforts, especially for preferred timber and charcoal species for which selective harvesting has had an impact on their distribution. Our results highlight the importance of rainfalls for the distribution of tree species in this seasonally dry region and calls for future research to forecast the impacts of climate change on habitat suitability.

Attribution analysis of the spatial variations in potential evapotranspiration on the Loess Plateau of China by a total differential equation

Abstract A total differential equation was proposed to assess the driving factors for the spatial variations in potential evapotranspiration (ET0). Using China's Loess Plateau as an example study area, three transects with distinct ET0 gradients in space, i.e., northwest–east, northwest–south and northwest–southwest, were chosen to sample spatially varied ET0 and four climatic variables (solar radiation, actual vapor pressure, wind speed, and mean temperature) at an interval of 10 km. Considered an independent variable, the distance was differentiated to quantify the contribution of each climatic variable to the spatial ET0 variations along each transect. A significant decrease in solar radiation and an increase in actual vapor pressure were identified as the dominant impact factors that led to a decreased ET0 in the northwest–east and northwest–south directions, respectively. As another key contributor, the decreasing wind speed induced a decreasing trend in ET0 from northwest to southwest. The above results implied that the dominant factor(s) for the spatial variations in ET0 differed among the regions. Therefore, the total differential equation is a powerful approach to determine the driving factors and to quantify their individual contribution to the spatial variations in ET0.

Ecohydrological controls on plant diversity in tropical South America

AbstractPlant species distribution is dominated by abundance and fluctuations of the available resources. Although diversity patterns along rainfall, latitudinal, and altitudinal gradients have been thoroughly examined, the role of hydrological processes in sustaining the resource availability critical to species richness is still poorly understood. Adopting soil moisture as a main limiting factor driving plant diversity in the tropics besides elevation, we propose a minimalist species richness model based on stochastic soil water balance and information theory. This work provides a novel approach to plant diversity modeling through a quantitative representation of the soil water balance, demonstrating the role of different modes of soil moisture temporal variability in the creation of ecohydrological niches. Using a single calibration parameter, the model captures the observed biodiversity patterns in tropical South America, effectively synthesizing the impacts of energy and water balances on species richness. We show that soil water abundance and variability are the strongest predictors of plant diversity in tropical South America besides elevation, with latitude and seasonal variation in potential evapotranspiration having a secondary effect. Excluding soil moisture abundance, seasonal and intraseasonal variability reduces model accuracy by 50, 48, and 64%. The importance of atmospheric humidity as an additional plant water resource creating niches for canopy species is also highlighted. Our results suggest that accounting not only for water abundance but also its variability is key to predicting biodiversity trends under future rainfall regimes.

Contribution analysis of the long-term changes in seasonal runoff on the Loess Plateau, China, using eight Budyko-based methods

Over the last five decades, runoff from the Loess Plateau has greatly decreased because of changes in the climate and intensive human activities. Comprehending and distinguishing the relative impacts of climate change and human activities on runoff is essential to adapt water-resource management and soil-and-water conservation projects to climate change. In this study, we used a technique involving integrated climate elasticity and eight Budyko-based methods to assess the relative impacts of climate change and human activities on runoff changes during high-flow and low-flow seasons in 17 catchments across the Loess Plateau during the period of 1961–2013. The results showed that, on average, runoff in the high-flow season exhibited a significant downward trend in 15/17 catchments, with an average decrease of 0.63mm/yr. In contrast, the decrease was 0.29mm/yr for the low-flow season. We also found that changes in runoff were more sensitive to variations in precipitation than variations in potential evapotranspiration, in both high-flow and low-flow seasons. The quantitative contributions from climate change and human activities as calculated by the eight Budyko-based methods were relatively similar during the high-flow season, but varied across catchments in the low-flow season. The results showed that, during the high-flow season, human activities had a greater impact on runoff changes than climate change, accounting for about 73% of the total decrease. However, in the low-flow season, which exhibits significantly increased potential evapotranspiration (p<0.01) and decreased precipitation, the influence of climate change on runoff changes was greater than the influence of human activities. The discrepancies between the results obtained via eight Budyko-based methods and the resulting uncertainties in the quantitative attributions are also discussed.

Sensitivity of Potential Evapotranspiration to Climate and Vegetation in a Water-Limited Basin at the Northern Edge of Tibetan Plateau

Potential evapotranspiration (PET) is important for both hydrological studies and water resources management, especially in arid regions. To better understand how PET varies due to the changing environment, analysis of the sensitivity of PET to climate and underlying surface characteristics is an important necessity. Based on gridded multi-source data sets, the present study estimated PET by using the Shuttleworth-Wallace model from 2000 to 2010 in the upstream and midstream areas of the Heihe River basin. Sensitivity coefficient and contribution coefficient of each parameter were calculated by the sensitivity coefficient method to quantitatively detect and compare the effect of changes in vegetation and climate exerted on the variation of PET. Results showed that: (1) PET varied greatly in the study area. Both climate and vegetation exert effects on the variation of PET; (2) PET is most sensitive to relative humidity in the study area. The sensitivity of PET to vegetation was also great and it increased with the decline of vegetation; (3) relative humidity contributed more to the intra-annual variation than other selected parameters. Vegetation indicated by LAI contribute more than net solar radiation. With this study, our understanding of variations of PET and its driving factors could be expanded from meteorological aspects to vegetation or ecological aspects, which is quite important for eco-hydrology and agricultural water resources management.

Trends in potential evapotranspiration from 1960 to 2013 for a desertification‐prone region of China

ABSTRACTEvapotranspiration is a sensitive parameter for assessing climate change. It controls energy and mass exchange and is a descriptor of drought in arid‐ and semi‐arid regions. Using the Mann–Kendall (M–K) test, Sen's slope estimator, and the stepwise regression, temporal, and spatial variations in potential evapotranspiration (ET0) and its dominant factors were analysed. The analysis was based on data from 173 meteorological stations in a desertification‐prone region of China over the period from 1960 to 2013. The annual ET0 decreased prior to 1990s and increased thereafter. The majority of stations had a decreasing ET0 trend, especially in summer, in which the average slope of all stations was −2.43 mm decade−1. Analysis of determining factors showed that a decrease in wind speed was the primary factor associated with decreasing ET0. The trend magnitude of ET0 increased from −2.25 mm decade−1 to −7.43 mm decade−1 as wind speed increased, then decreased to −3.00 mm decade−1. Decreasing ET0 and increasing P in the western region led to decrease in the aridity index, suggesting a wetter climate and reduced desertification. Increasing aridity index in the eastern region reduced the vegetation cover and facilitated desertification processes, which might be a disadvantage for ecological reconstruction and desertification control. Better understanding of the response of ET0 to regional climate change may facilitate efficient use of limited water resources and establish management strategies that can combat desertification and maintain ecological security in a desertification‐prone region.

Environmental drivers of the spatiotemporal dynamics of respiratory syncytial virus in the United States.

Epidemics of respiratory syncytial virus (RSV) are known to occur in wintertime in temperate countries including the United States, but there is a limited understanding of the importance of climatic drivers in determining the seasonality of RSV. In the United States, RSV activity is highly spatially structured, with seasonal peaks beginning in Florida in November through December and ending in the upper Midwest in February-March, and prolonged disease activity in the southeastern US. Using data on both age-specific hospitalizations and laboratory reports of RSV in the US, and employing a combination of statistical and mechanistic epidemic modeling, we examined the association between environmental variables and state-specific measures of RSV seasonality. Temperature, vapor pressure, precipitation, and potential evapotranspiration (PET) were significantly associated with the timing of RSV activity across states in univariate exploratory analyses. The amplitude and timing of seasonality in the transmission rate was significantly correlated with seasonal fluctuations in PET, and negatively correlated with mean vapor pressure, minimum temperature, and precipitation. States with low mean vapor pressure and the largest seasonal variation in PET tended to experience biennial patterns of RSV activity, with alternating years of “early-big” and “late-small” epidemics. Our model for the transmission dynamics of RSV was able to replicate these biennial transitions at higher amplitudes of seasonality in the transmission rate. This successfully connects environmental drivers to the epidemic dynamics of RSV; however, it does not fully explain why RSV activity begins in Florida, one of the warmest states, when RSV is a winter-seasonal pathogen. Understanding and predicting the seasonality of RSV is essential in determining the optimal timing of immunoprophylaxis.

Spatial and Decadal Variations in Potential Evapotranspiration of China Based on Reanalysis Datasets during 1982–2010

Potential evapotranspiration (PET) is an important indicator of atmospheric evaporation demand and has been widely used to characterize hydrological change. However, sparse observations of pan evaporation (EP) prohibit the accurate characterization of the spatial and temporal patterns of PET over large spatial scales. In this study, we have estimated PET of China using the Penman-Monteith (PM) method driven by gridded reanalysis datasets to analyze the spatial and decadal variations of PET in China during 1982–2010. The results show that the estimated PET has decreased on average by 3.3 mm per year (p &lt; 0.05) over China during 1982–1993, while PET began to increase since 1994 by 3.4 mm per year (p &lt; 0.05). The spatial pattern of the linear trend in PET of China illustrates that a widely significant increasing trend in PET appears during 1982–2010 in Northwest China, Central China, Northeast China and South China while there are no obvious variations of PET in other regions. Our findings illustrate that incident solar radiation (Rs) is the largest contributor to the variation of PET in China, followed by vapor pressure deficit (VPD), air temperature (Tair) and wind speed (WS). However, WS is the primary factor controlling inter-annual variation of PET over Northwest China.

Changing forest water yields in response to climate warming: results from long-term experimental watershed sites across North America.

Climate warming is projected to affect forest water yields but the effects are expected to vary. We investigated how forest type and age affect water yield resilience to climate warming. To answer this question, we examined the variability in historical water yields at long-term experimental catchments across Canada and the United States over 5-year cool and warm periods. Using the theoretical framework of the Budyko curve, we calculated the effects of climate warming on the annual partitioning of precipitation (P) into evapotranspiration (ET) and water yield. Deviation (d) was defined as a catchment's change in actual ET divided by P [AET/P; evaporative index (EI)] coincident with a shift from a cool to a warm period – a positive d indicates an upward shift in EI and smaller than expected water yields, and a negative d indicates a downward shift in EI and larger than expected water yields. Elasticity was defined as the ratio of interannual variation in potential ET divided by P (PET/P; dryness index) to interannual variation in the EI – high elasticity indicates low d despite large range in drying index (i.e., resilient water yields), low elasticity indicates high d despite small range in drying index (i.e., nonresilient water yields). Although the data needed to fully evaluate ecosystems based on these metrics are limited, we were able to identify some characteristics of response among forest types. Alpine sites showed the greatest sensitivity to climate warming with any warming leading to increased water yields. Conifer forests included catchments with lowest elasticity and stable to larger water yields. Deciduous forests included catchments with intermediate elasticity and stable to smaller water yields. Mixed coniferous/deciduous forests included catchments with highest elasticity and stable water yields. Forest type appeared to influence the resilience of catchment water yields to climate warming, with conifer and deciduous catchments more susceptible to climate warming than the more diverse mixed forest catchments.