Droughts In Semi-arid Regions Research Articles

Assessing sand dams for contributions to local water security and drought resilience in the semi-arid eastern Shashe catchment, Zimbabwe

Climate change is increasing the frequency and severity of droughts in semi-arid regions. Small-scale water storage can help build drought resilience, particularly in rural areas with no access to formal water infrastructure. Sand dams, which store water by capturing water in sand-filled ephemeral rivers during the wet season, are one promising storage option. While emerging studies indicate tentative evidence of their benefits, the focus on resilience is under-addressed. This study evaluates the impact of sand dams on resilience to climate variability and changes through a participatory case study approach in the Shashe catchment, a semi-arid catchment shared by Botswana and Zimbabwe. Participatory research was conducted via site inspections, focus group discussions, and interviews at 20 sand dams utilized by 19 villages across the Zimbabwean portion of the Shashe catchment. The results show that sand dams significantly improved local water availability, most notably with a significant increase in the number of months per year that water could be collected from the dam site (mean = 6.5 months before, to mean = 10.9 months after construction, p < 0.05). This increase is also reflected in drought years (mean = 5.8 months before, to mean = 9.6 months after construction, p < 0.05). Sand dams also contribute to the adaptive capacity of communities via key benefits such as diversification of livelihood activities, improved health and hygiene, and reduced erosion in the surrounding area due to increased vegetation. In sum, the study demonstrates clear benefits to communities facing drought, supporting calls to elevate sand dams on the development agenda.

A shift from isohydric to anisohydric water-use strategy as a result of increasing drought stress for young apple trees in a semiarid agroforestry system

Prolonged drought due to global warming can have significant effects on tree growth and sustainability by changing physiological traits. Agroforestry is considered climate-smart and can help buffer the effects of extreme climates. However, it remains unclear as to how trees in agroforestry physiologically adapt to prolonged drought in semiarid regions. Here, we report results from a three-year rainfall exclusion experiment (an extreme natural drought occurred during the experiment) designed to understand the physiological mechanism of young apple trees responding to different degrees of prolonged drought (moderate drought by reducing rainfall by 15% and severe drought by reducing rainfall by 25%) in an alley agroforestry system constituting of apple trees and oil crops. We found that the measured physiological traits for young apple tree under agroforestry were not clearly different from those under monoculture, although soil water content in the top 80 cm was reduced by 9.3%. Under moderate drought conditions, the apple trees in agroforestry implemented a conservative water-use strategy. Stomatal conductance, photosynthesis, and leaf transpiration were reduced by 15.5%, 3.8%, and 12.6%, respectively, whereas pre-dawn (Ψpd) and midday (Ψmd) leaf water potential stabilized, indicating a clear isohydric behavior. Under severe drought conditions, however, the apple trees still maintained normal stomatal opening to significantly (p<0.01) increase photosynthesis (9.8%) and leaf transpiration (12%) at the expense of reducing Ψpd (58.1%) and Ψmd (25.4%), showing anisohydric behavior which can place apple trees at risk. Reduction of aboveground biomass and greater numbers of fine roots in deeper soils to explore deep-layer soil water could explain such risky behavior by apple trees suffering severe drought. The findings here provide new insights into the mechanism through which the coordination between canopy water consumption and aboveground/belowground biomass redistribution of trees underpin the physiological adaptation of trees to different degrees of prolonged drought in semiarid regions.

Prediction of Hydrological Drought in Semi-arid Regions Using a Novel Hybrid Model

Prediction of Hydrological Drought in Semi-arid Regions Using a Novel Hybrid Model

Assessment and monitoring of meteorological and hydrological drought in semiarid regions: The Wadi Ouahrane basin case study (Algeria)

The aim of this study is to use the Standardized Precipitation Index (SPI) and the Standardized Runoff Index (SRI) to investigate meteorological and hydrological drought in the Wadi Ouahrane basin of north Algeria. Indeed, in recent years, the Wadi Ouahrane basin has suffered from persistent and recurrent meteorological and hydrological droughts, which caused large economic losses and extreme difficulties for the local population, resulting in widespread out-migration and poverty throughout the country. In order to evaluate the SPI, 6 monthly rainfall series for the period 1972–2018 have been considered. Moreover, with the aim to evaluate the SRI, monthly runoff data from 1972 to 2018 were also collected in one station. Both the SPI and the SRI have been evaluated at 1-, 3-, 6-, 9-, 12- and 24-month timescales. Although a similar percentage of positive and negative values of both the indices has been detected for the different timescales, the temporal distribution of these values allowed us to identify the periods characterized by severe or extreme drought conditions such as 1982, the end of 1983, 1987–1990, 1992–1995 and, recently, 2014–2016. Finally, in order to detect drought temporal evolution in the period 1972–2018, the SPI and SRI series at the different multi-times scales were tested for trends through the Theil-Sen estimator (SS), the Mann–Kendall test (MK), the Modified Mann–Kendall test (MMK) and the Innovative Trend Method (ITA). As a result, although the SS evidenced negative values, the MK test did not show significant trends thus indicating stable drought conditions.

Species mixing enhances the resistance of Robinia pseudoacacia L. to drought events in semi-arid regions: Evidence from China's Loess Plateau

As a potential planting strategy, species mixing increases biomass production, improves ecosystem service functions, and mitigates climate change. However, the effect of species mixing on tree growth and drought resilience in semi-arid areas remains unclear. Hence, we established tree-ring chronologies of Robinia pseudoacacia L. in pure Robinia pseudoacacia L. plantation (RP) and mixed plantations with Hippophae rhamnoides L. and Populus simonii Carr. at different proportions of 8:2 and 5:5 (RH 8:2, RH 5:5, RC 8:2, RC 5:5) in the typical semi-arid region of the Loess Plateau (LP), China. The mean annual growth, climate-growth relationships, and tree resilience (Rs) to drought, including resistance (Rt) and recovery (Rc), were analyzed using dendrochronological methods. The results showed that the growth of R. pseudoacacia L. in mixed plantations was lower when Palmer Drought Severity Index (PDSI) >0, but much higher than that in monoculture under drought stress (PDSI <0 or after drought event). Meanwhile, the relationship between PDSI and tree growth was significantly positive in the pure plantation, but weakened in the mixed plantations, indicating that species mixing alleviated drought stress to some extent. The resilience results showed that, although the Rc was higher in monoculture after drought events, species mixing could enhance Rt and mitigate the growth decline of R. pseudoacacia L. during drought events. Moreover, the Rt varied significantly among mixing species and proportions and was also affected by the magnitude and timing of drought. The RC 5:5 and RH 8:2 had higher resistance to moderate and severe drought stress. However, RC 8:2 and RH 5:5 could cope better with mild drought stress. These results indicate that species mixing can alleviate drought stress and improve the drought resistance. Therefore, it is necessary to expand species mixing to maximize plantation functions and minimize the potential impacts of warming and drought in semi-arid regions.

Meteorological drought in semi-arid regions: A case study of Iran

Meteorological drought in semi-arid regions: A case study of Iran

Sustainable long‐term mitigation of floods and droughts in semiarid regions: Integrated optimal management strategies for a salt lake basin

AbstractWe present a management project for the mitigation of extreme climatic events in the frame of cyclic wet and dry periods in the semiarid Pampean region of Argentina. The developed methodological approach allows quantitative planning of strategies to tackle the effect of recurrent floods and droughts in a salt lake basin through the formulation of an optimal control problem, which constitutes a novel approach to ecohydrological systems management. The control variables correspond to (i) diversion flows from a lake tributary to an artificial freshwater reservoir to damp lake flooding, (ii) freshwater flows from the reservoir to the salt lake to keep its salinity at desired values and (iii) freshwater flows to irrigate crops during drought periods. Further, we address the economic valuation of ecosystem services in the basin. Quantitative results provide useful insights on optimal management strategies and the effects of their implementation, as well as their impact on the valuated services in the watershed under study.

Morphological trait as a determining factor for Populus simonii Carr. to survive from drought in semi-arid region

Widespread tree mortality induced by drought events causes significant damage to the local ecosystem and society. Populus simonii Carr. in Zhangbei, Bashang region, China, which was the dominant species of local shelter forest, experienced a wide and heterogeneous dieback, calling for an urgent need for research revealing the mechanism of this mortality event. We conducted a field survey across the county examining 443 poplar individuals with different degrees of degradation. Basic morphological tree data and tree-ring samples were obtained and analysed. The stable water isotope technique was also applied to predict the water use pattern and rooting depth. Long-term climate data were analysed and the self-calibrating Palmer drought severity index (scPDSI) was calculated. The main results were as follows: 1) The growth rate of diameter at breast height (DBH) and tree height began to decrease after the year 2000; however, this drawback effect tended to be stronger for poplars with a higher degradation degree. The results also showed that the poplars that survived were inherently larger in size. 2) Following the increase in the degree of degradation, poplars gradually lost their ability to absorb deep soil water, putting them into a more stressful water condition. We concluded that ageing and stand density were not the major effects but drought accounted for the mortality event. Larger poplars with deeper root systems tended to be more resistant to drought. Local water resource management is also vital for shelterbelt forests to survive and grow.

Hillslope geodiversity improves the resistance of shrubs to prolonged droughts in semiarid ecosystems

Geodiversity effects on ecosystem productivity were investigated using remotely sensed data and a mathematical model, by introducing a spatially non-uniform surface-water infiltration. Two hillslope types, with different geodiversity levels, as determined by the soil depth and stoniness, were selected for this study. Low-geodiversity hillslopes (‘homogenous hillslopes’) were identified by their dense herbaceous vegetation cover, and lack of rock fragments cover. High-geodiversity hillslopes (‘heterogeneous hillslopes’) are characterized by a more sparse cover of herbaceous vegetation, and relatively high rock fragment cover (>20%). Calculating Soil Water Index (SWI) from Landsat-5 TM, Landsat-7 ETM+ (SLC-ON) and Landsat-8 satellite images for the years 1994–2017 shows that during most of these years, SWI was higher at the heterogeneous hillslopes. This was particularly prominent after 2009 when mass mortality of shrubs took place on the homogenous hillslopes but not in the heterogeneous ones. Numerical simulations show that after a prolonged drought, the vegetation in the homogenous system dried out, and the system did not recover even after the yearly rainfall amounts returned to normal. In the heterogeneous system, the vegetation patches survived the drought episode and then recovered. This demonstrates the crucial role played by hillslope geodiversity in determining the durability of vegetation under prolonged droughts in semiarid regions.

Concentration of Traces Metals in Underground Dams in the Semi-Arid of the Rio Grande do Norte State, Brazil: Case Study of the Sub-Basin of the Cobras River

Several studies were carried out and drought coexistence technologies were developed to deal with the problem of drought in semiarid regions, such as the construction of underground dams, which became a tool for rural development, mainly for family agriculture. However, there are still scarce informations regarding technical studies on the water security level of underground dams, especially about trace metal contamination due to the use and agricultural occupation of the soils downstream of the dams. In this work, the level of contamination of trace metals in waters of underground dams, during two hydrological years, was evaluated around of the sub-basin of the Cobras river, in the Rio Grande do Norte state, Brazil. The analysis of the results indicated that the water samples stored in the Alexandre and Ginaldo underground dams are within the permitted drinking patterns and did not suffer, on the other hand, any alteration in their quality that requires treatment for human consumption, fitting into Class 1. Most of the samples from the waters of the Boa Vista and Ademar dams are above the maximum allowable value for iron (Fe), lead (Pb), chromium (Cr), and nickel (Ni), requiring a differentiated treatment for human consumption, and can be classified as Class 2. The probable contamination of the waters stored in the underground dams may be of geological origin, since the largest accumulation of trace metals occurred in the lower area of the river course greater drained area, leading to believe that the metals come from the rock weathering that make up the geological framework of the region.

Qinghai spruce (Picea crassifolia) and Chinese pine (Pinus tabuliformis) show high vulnerability and similar resilience to early-growing-season drought in the Helan Mountains, China

Abstract Understanding the mechanisms for how tree growth responds to drought is important for forest conservation and management in semi-arid regions, particularly under ongoing climate change. However, most previous studies have been relied on linear statistical analysis, unsupported by insights into tree physiological processes. In this study, we applied process-based Vaganov–Shashkin (VS) model to investigate the stem radial growth response and resilience of Qinghai spruce (Picea crassifolia) and Chinese pine (Pinus tabuliformis) to intense drought in semi-arid region of China from 1960 to 2013. Correlation analysis indicated that soil moisture availability in the early growing season (May to July) significantly limit stem growth for both tree species, but Chinese pine was affected more strongly by drought legacies. The model results validated our statistical modeling results, and quantified the effects of temperature and soil moisture on the intra-seasonal variation of the relative stem radial growth rate. The influence of soil moisture on the relative stem radial growth rate during the early growing season was significantly higher for positive pointer years (years with greater than mean growth) than for negative pointer years (years with less than mean growth) for both tree species. Interestingly, the two species displayed similar patterns of growth resilience in response to drought. Based on our successful application of the VS model, our results provide important insights into the two main tree species in the semi-arid Helan Mountains, and offer a new perspective on tree growth processes and their varying responses and resilience to drought.

Changing characteristics of meteorological droughts in Nigeria during 1901–2010

The objective of this study was to assess the changes in the severity and return periods of meteorological droughts during major cropping seasons of Nigeria for the period 1901–2010 in order to understand the impacts of climate variation on seasonal droughts. Gauge-based gridded global precipitation climatology center (GPCC) rainfall and climate research unit (CRU) potential evapotranspiration (PET) data having a spatial resolution of 0.5° were used for the reconstruction of droughts using standardized precipitation evapotranspiration index (SPEI). SPEI values were fitted with the best distribution function to estimate seasonal droughts return periods and the modified Mann-Kendall test was used to assess the secular changes in climate variables and drought index. The temporal variations in droughts and their interrelations with rainfall and temperature trends were assessed using a 50-year moving window with a 10-year time step. The results showed that meteorological drought severity has increased for all the cropping seasons of Nigeria. Temperature was found to be the dominating factor for defining droughts in semi-arid regions in the north while rainfall in the monsoon and tropical savanna climatic zones dominates in the south. Rises in temperature in the range of 0.14–0.42 °C/decade and almost no change in rainfall have caused decreases in SPEI up to −0.25/decade in some regions. The number of grid points with decreasing SPEI was found to vary between 50 out of 323 for millet and 152 for yam growing season. The moderate droughts were found to become more frequent compared to other classes of droughts. Amongst the cropping seasons, the highest increases in drought frequency were observed during corn growing season. The highest decrease in the median value of the return period of moderate, severe and extreme droughts during the two corn growing seasons were observed to be 6.25, 12.86 to 13.20, 23.15 to 24.31 years in 1901–1950 to 6.25, 12.92 to 12.94, 23.51 to 23.64 in 1961–2010. Compared to other drought severities, the return periods of the moderate droughts were found to decrease more. A general decrease in the return periods of droughts indicates more frequent droughts during all cropping seasons of Nigeria. Therefore, it can be concluded that the rising temperature due to global warming would increase drought severity and frequency in all the cropping seasons of Nigeria.

Does climate adaptation of vulnerable households to extreme events benefit livestock production?

Extreme climate events have become more frequent and severe as a result of climate change. In semi-arid pastoral regions, extreme drought is harmful to livestock production and to vulnerable human communities and livelihoods. In this study, we considered extreme drought in semi-arid regions and investigated climate adaptations taken by the local vulnerable households and their effects on livestock production. We first analyzed the characteristics of spatio-temporal variation of extreme drought in Hulun Buir, Inner Mongolia, China, during 1980–2015 by using the FAO Penman–Monteith model and then applied stochastic frontier analysis to evaluate the technical efficiency of livestock production of 126 pasturing households. We further explored the effects of climate adaptations to extreme drought on the technical efficiency of livestock production. The results showed that the average frequency of extreme drought in Hulun Buir was 4.6 month/year and displayed a decreasing trend varying from southwest to northeast during 1980–2015. Based on the survey data, the average technical efficiency of livestock production of the local households was 0.530 in 2015, which could be greatly improved. The adaptations of the households significantly positively increased the technical efficiency of livestock production. Purchasing more forage and selling more livestock were the two most frequently adopted and effective adaptive measures for the response of vulnerable households in Hulun Buir to extreme drought risks. Further policy options were provided to improve livestock production as well as rangeland protection and restoration for coping with extreme drought in the context of climate change in semi-arid pastoral regions.

The Response of Vegetation Phenology and Productivity to Drought in Semi-Arid Regions of Northern China

A major disturbance in nature, drought, has a significant impact on the vulnerability and resilience of semi-arid ecosystems by shifting phenology and productivity. However, due to the various disturbance mechanisms, phenology and primary productivity have remained largely ambiguous until now. This paper evaluated the spatio-temporal changes of phenology and productivity based on GIMMS NDVI3g time series data, and demonstrated the responses of vegetation phenology and productivity to drought disturbances with the standardized precipitation evapotranspiration index (SPEI) in semi-arid ecosystems of northern China. The results showed that (1): vegetation phenology exhibited dramatic spatial heterogeneity with different rates, mostly presented in the regions with high chances of land cover type variation. The delayed onset of growing season (SOS) and advanced end of growing season (EOS) occurred in Horqin Sandy Land and the eastern Ordos Plateau with a one to three days/decade (p &lt; 0.05) rate and in the middle and east of Inner Mongolia with a two days/decade rate, respectively. Vegetation productivity presented a clear pattern: south increased and north decreased. (2) Spring drought delayed SOS in grassland, barren/sparsely vegetated land, and cropland, while autumn drought significantly advanced EOS in grassland and barren/sparsely vegetated lands. Annual drought reduced vegetation productivity and the sensitivity of productivity regarding drought disturbance was higher than that of phenology.

Water volume reduction increases eutrophication risk in tropical semi-arid reservoirs

Abstract Aim Global patterns of temperature and precipitation have significantly changed over the last century and nearly all predictions point to even greater changes by the end of 2100. Long periods of drought in semi-arid regions generally reduce reservoirs and lakes water level, increasing the nutrients concentrations in the water. Our principal hypothesis is that water volume reduction, driven by prolonged droughts, will increase reservoirs susceptibility to eutrophication and accordingly an increase in trophic state. To test this hypothesis, we used a comparative analysis of ecosystems in a space-for-time substitution approach, in a Brazilian semi-arid region, to predict the consequences of reservoirs water volume reduction on key limnological variables. Methods We sampled 16 reservoirs located in two sub-basins with contrasting rainfall regimes, inserted on Piranhas-Açu watershed. The Seridó River basin (SB) is dry and the Piancó River basin (SB) is humid, with annual mean precipitation of 500 and 700 mm, respectively. Linear regressions analyzes were performed to assess whether the percentage of maximum volume stored (%MVS) is a good predictor for total phosphorus (TP), total nitrogen (TN) and chlorophyll-a (CHLA). In addition, a two factorial analysis of variance (two-way ANOVA) was performed to test for period (dry, very dry and extremely dry), basin (SB and PB) and their interactions effects on TP, TN, CHLA, conductivity, turbidity, and Secchi depth. Results The results showed a reduction in the reservoirs %MVS both for PB and SB regions. At the extremely dry period, all reservoirs were classified as eutrophic, but TP concentrations reached much higher values in SB than in PB. The linear regressions analyses showed that the TP and TN were negatively related to %MVS during all periods sampled. The two-way ANOVA showed that there were significant basin and period effects on TP, TN, Secchi depth and turbidity, whereas for CHLA and conductivity only basin effects were observed. In addition, we found significant interaction effects between period and basin on TP, TN and turbidity. Conclusions We conclude that the contrasting levels of rainfall observed between the two basins affect the water quality and trophic state of the reservoirs and these effects are magnified by water volume reduction. Therefore, our findings might help to predict the consequences of rainfall reductions on freshwater ecosystems of Brazilian drylands.

Past and future drought in Mongolia.

The severity of recent droughts in semiarid regions is increasingly attributed to anthropogenic climate change, but it is unclear whether these moisture anomalies exceed those of the past and how past variability compares to future projections. On the Mongolian Plateau, a recent decade-long drought that exceeded the variability in the instrumental record was associated with economic, social, and environmental change. We evaluate this drought using an annual reconstruction of the Palmer Drought Severity Index (PDSI) spanning the last 2060 years in concert with simulations of past and future drought through the year 2100 CE. We show that although the most recent drought and pluvial were highly unusual in the last 2000 years, exceeding the 900-year return interval in both cases, these events were not unprecedented in the 2060-year reconstruction, and events of similar duration and severity occur in paleoclimate, historical, and future climate simulations. The Community Earth System Model (CESM) ensemble suggests a drying trend until at least the middle of the 21st century, when this trend reverses as a consequence of elevated precipitation. Although the potential direct effects of elevated CO2 on plant water use efficiency exacerbate uncertainties about future hydroclimate trends, these results suggest that future drought projections for Mongolia are unlikely to exceed those of the last two millennia, despite projected warming.

Evaluating the Characteristics of Multiyear Extreme Droughts in Semi-Arid Regions

Following the unconditional definition of drought events, this study presents general mathematical expressions that can be used to evaluate the occurrence probability and the return period of multiyear drought events of extreme magnitude evolved after truncating low order dependent hydrological or meteorological processes. The drought magnitude was fitted using the gamma distribution and the drought run length was defined unconditionally regardless where the run starts as long as it satisfies the continuity. Considering the joint analysis of the drought magnitude and the run length, the characteristics of the multiyear drought of extreme magnitude achieved theoretically was found to match well with empirical results obtained after analyzing the simulated and historical precipitation. After truncating the annual rainy season precipitation for Madaba region in Jordan, the 6-year extreme historical drought that occurred in 1958–1963 was a rare event recurring every 226 years. In the semi-arid region of Madaba, meteorological drought events of a short duration, 2–3 years, and a precipitation deficit of 149 mm or less are frequent events with 7–10 years return period, while events of 4 years or more, tested at deficit threshold of 149 mm, are less frequent events regardless of their magnitude.

Enhancing soil drought induced by climate change and agricultural practices: Observational and experimental evidence from the semiarid area of northern China

Increased water scarcity has led to a decade-long soil drought in the semiarid area of northern China, which caused food insecurity in this region. However, there is a lack of sufficient observational evidence about how climate change and agricultural practices have interactively affected this soil drought. Long-term in situ soil moisture measurements collected in agricultural experimental plots indicate that the mean temperature and precipitation during the growing season have reduced soil moisture by 11.2%, and agricultural practices have aggravated the soil drying trend in the 0–100mm soil layer over the past three decades. Our results also show that planting water-expensive crops (e.g., potato and maize) may aggravate soil drought. Crop rotation increases soil water consumption by 8.9–12.6% over continuous cropping. Excessive fertilizer use increases water consumption by 25.4–46.9% and decreases the water use efficiency (WUE) by 14.6–35.3%, while tillage accounts for the consumption of 10.3% more soil moisture than no-tillage. Our results indicate that agricultural practices, including crop rotation, a high fertilizer input, and tillage, may increase water consumption and aggravate soil drying. Our findings call for effective strategies for mitigating soil drought in semiarid regions, such as an adjustment of the cropping system, reduced fertilizer use, and improved conservation tillage.

Analysis of Rainfall in Assessing the Drought in Semi-arid Region of Karnataka State, India

The present study focuses on drought analysis with an aim to understand the drought vulnerability, estimate and map the drought duration and severity in drought prone North Interior Karnataka region, India. A detailed analysis were carried out using rainfall data of more than 178 (with greater than 30 years data) stations to understand the drought characteristics. Rainfall descriptive variability, percentage occurrence of drought incidences and spatial distribution of rainfall were derived. In order to evaluate the drought severity and its extent and to map, method proposed by Ponce et al. (2000) and the Geographic Information System has been used. The method by Ponce et al. (2000) characterize drought based on intensity, duration and recurrence interval using mean annual precipitation of a location. The results obtained for the study area indicate that, the region is mostly semi-arid with drought occur for more than 50 % of the time. The majority of the drought events are of moderate intensity with few extreme intensity events. Further, it is noticed that, in many station, the rainfall show a decreasing trend. Since, rainfall in this region are mostly declining due to climatic change, the area would experience increasing drought severity in the forthcoming years. The outcome of the study would be useful in understanding the drought pattern, severity and extent in the study area which can be used by scientists and water management professionals to plan drought mitigation measures.

From leaf to whole-plant water use efficiency (WUE) in complex canopies: Limitations of leaf WUE as a selection target

Plant water use efficiency (WUE) is becoming a key issue in semiarid areas, where crop production relies on the use of large volumes of water. Improving WUE is necessary for securing environmental sustainability of food production in these areas. Given that climate change predictions include increases in temperature and drought in semiarid regions, improving crop WUE is mandatory for global food production. WUE is commonly measured at the leaf level, because portable equipment for measuring leaf gas exchange rates facilitates the simultaneous measurement of photosynthesis and transpiration. However, when those measurements are compared with daily integrals or whole-plant estimates of WUE, the two sometimes do not agree. Scaling up from single-leaf to whole-plant WUE was tested in grapevines in different experiments by comparison of daily integrals of instantaneous water use efficiency [ratio between CO2 assimilation (AN) and transpiration (E); AN/E] with midday AN/E measurements, showing a low correlation, being worse with increasing water stress. We sought to evaluate the importance of spatial and temporal variation in carbon and water balances at the leaf and plant levels. The leaf position (governing average light interception) in the canopy showed a marked effect on instantaneous and daily integrals of leaf WUE. Night transpiration and respiration rates were also evaluated, as well as respiration contributions to total carbon balance. Two main components were identified as filling the gap between leaf and whole plant WUE: the large effect of leaf position on daily carbon gain and water loss and the large flux of carbon losses by dark respiration. These results show that WUE evaluation among genotypes or treatments needs to be revised.