Ecosystem water-use efficiency (WUE) is defined as the ratio of carbon gain (i.e., gross primary productivity; GPP) to water consumption (i.e., evapotranspiration; ET). WUE is markedly influential on carbon and water cycles, both of which are fundamental for ecosystem state, climate and the environment. Drought can affect WUE, subsequently disturbing the composition and functionality of terrestrial ecosystems. In this study, the impacts of drought on WUE and its components (i.e., GPP and ET) are assessed across the Contiguous US (CONUS) at fine spatial and temporal resolutions. Soil moisture simulations from land surface modeling are utilized to detect and characterize agricultural drought episodes and remotely sensed GPP and ET are retrieved from the moderate resolution imaging spectroradiometer (MODIS). GPP, as the biome vitality indicator against drought stress, is employed to investigate drought recovery and the ecosystems’ required time to revert to pre-drought condition. Results show that drought recovery duration indicates a positive correlation with drought severity and duration, meaning that a protracted drought recovery is more likely to happen following severe droughts with prolonged duration. WUE is found to almost always increase in response to severe (or worse) drought episodes. Additionally, ET anomalies are negatively correlated with drought severity and ET is expected to decrease during severe (or worse) drought episodes. Lastly, the changes of WUE are decomposed in relation to its components and the cross-relation among the variables is revealed and a consistent changing pattern is detected.

In northern regions, like Finland, peak river discharge is principally controlled by maximum snowmelt runoff during spring (March–May). Global warming and climate change extensively influence both the quantity and temporal characteristics of peak discharge in northern rivers by altering snowpack accumulation and melt processes. This study analyzed peak spring flood discharge (PSFD) magnitude (PSFDM) and timing (PSFDT) in four natural rivers (Simojoki, Kuivajoki, Kiiminkijoki, and Temmesjoki) across northern Finland, in terms of long-term (1967–2011) variability, trends, and links to large-scale climate teleconnections. The PSFDM significantly (p < 0.05) declined in the Simojoki, Kuivajoki, and Kiiminkijoki rivers over time. Both the Simojoki and Kuivajoki rivers also experienced significant decreasing trends of about −0.33 and −0.3 (days year⁻¹), respectively, in the PSFDT during 1967–2011. In these two rivers, the less and earlier PSFDs were principally attributable to the warmer spring seasons positively correlated with the North Atlantic Oscillation (NAO) in recent decades. Moreover, daily precipitation time series corresponding to the PSFD events showed no considerable effects on PSFDM and PSFDT changes in all the natural rivers studied. This suggests that less and earlier historical PSFDs in natural rivers at higher latitudes in northern Finland were primarily induced by warmer springtime temperatures influencing snowpack dynamics.

Societies are facing major challenges in allocating water resources to growing water demands due to population growth and industrial and agricultural developments. With increasing water scarcity, the need to increase agricultural water productivity is receiving significant attention in developing countries. Among alternative options for meeting increasing water demand, improving productivity has received considerable attention. Therefore, planning of water systems to face future development conditions needs further studies on land, water use, and resources as well as consideration of objectives to maximize crop production to achieve the maximum net return. Because climate change is likely to have impact on the hydrological cycle and consequently on the available water resources and agricultural water demand, there are concerns about the effects of climate change on agricultural productivity. Considering climate change impacts, in order to optimize agricultural productivity, practical frameworks and models based on comprehensive researches and studies need to be developed. The goal of this study is to develop an agricultural planning model in order to optimize the cultivated area, crop pattern, and irrigation efficiency based on the estimations of crop water requirements, water availability, and water allocation to irrigation. For this purpose, the Aharchay watershed located in the northwestern part of Iran is selected as the case study. For crop water requirement estimation, the output of an atmosphere-ocean general circulation model statistically downscaled and used as inputs to a computer model. Then water supply resources are assessed using a water allocation planning tool. The results of this study show the significance of integration and using different tools and methods in assessing and allocating water resource in regions with limited or scarce water resources.

Understanding the atmospheric circulation patterns (ACPs) influencing drought development is important in management of this spatially extensive and recurrently prolonged natural hazard. Using the Standardized Precipitation Evapotranspiration Index (SPEI), this study evaluates the spatio‐temporal variability in climatological drought dynamics (in terms of intensity, frequency, duration, and extension) in Finland in 1962–2011. The SPEI values are calculated in 12‐, 3‐, and 1‐month time steps (SPEI‐12, ‐3, and ‐1, respectively) and the analyses are based on annual (SPEI‐12Ann), seasonal (e.g. SPEI‐3Win for winter), and monthly (e.g. SPEI‐1Dec for December) time scales. The relationships between SPEI values and well‐known ACPs of climate variability over Finland are also investigated. Our analysis shows that on national scale, the longest observed drought is 12 months (October 2002–September 2003) observed in SPEI‐12 values. Droughts intensify in April, August, and September, and largely occur over the south, centre, east, and west of Finland. December has the highest frequency of droughts, but with significant wetting trends. Analysis of annual SPEI‐12 indicates an increase in the probability of drought extent over time. In warm months (April–September), influential ACPs for temperature variability and drought conditions are mainly the Arctic Oscillation (AO) and the Scandinavia pattern. For the cold months (October–March), the AO, the North Atlantic Oscillation, the East Atlantic, and the Polar patterns influence precipitation deficit and SPEI. Although Finland has experienced wetting trends during the period 1962–2011, this study provides a detailed spatial assessment of climatological drought variability and the plausible atmospheric circulation drivers for the boreal environment of Finland in recent decades.