Different Effects of Irrigation in Dry and Wet Years in the U.S. Great Plains

The relationship of δD and δ18O in soil water and its implications for soil evaporation across distinct rainfall years in winter wheat field in the North China Plain

A novel approach to recognize the long-term spatial-temporal pattern of dry and wet years over Iran

This study highlights the influence of convectively coupled Kelvin wave (KW) activity on deep convection and African easterly waves (AEWs) over North Africa during dry and wet boreal summer rainfall years. Composite analysis based on 25 years of rainfall, satellite observed cold cloud temperature, and reanalysis data sets show that KWs are more frequent and stronger in dry Central African years compared with wet years. Deep convection associated with KWs is slightly more amplified in dry years compared with wet years. Further, KW activity over North Africa strengthens the lower level zonal flow and deepens the zonal moisture flux in dry years compared with wet years. Results also show that enhanced KW convection is in phase with above-average AEW variance in dry years. However, enhanced KW convection is out-of-phase with average AEW activity in wet years. In general, this study suggests that KW passage over Africa enhances convective activity and more strongly modulates the monsoon flow and moisture flux during the dry years than wet years.

Plant phenology is the most sensitive biological indicator that responds to climate change. Many climate models predict that extreme precipitation events will occur frequently in the arid areas of northwest China in the future, with an increase in the quantity and unpredictability of rain. Future changes in precipitation will inevitably have a profound impact on plant phenology in arid areas. A recent study has shown that after the simulated enhancement of precipitation, the end time of the leaf unfolding period of Nitraria tangutorum advanced, and the end time of leaf senescence was delayed. Under extreme climatic conditions, such as extremely dry or wet years, it is unclear whether the influence of the simulated enhancement of precipitation on the phenology of N. tangutorum remains stable. To solve this problem, this study systematically analyzed the effects of the simulated enhancement of precipitation on the start, end and duration of four phenological events of N. tangutorum, including leaf budding, leaf unfolding, leaf senescence and leaf fall under extremely dry and wet conditions. The aim of this study was to clarify the similarities and differences of the effects of the simulated enhancement of precipitation on the start, end and duration of each phenological period of N. tangutorum in an extremely dry and an extremely wet year to reveal the regulatory effect of extremely dry and excessive amounts of precipitation on the phenology of N. tangutorum. (1) After the simulated enhancement of precipitation, the start and end times of the spring phenology (leaf budding and leaf unfolding) of N. tangutorum advanced during an extremely dry and an extremely wet year, but the duration of phenology was shortened during an extremely wet year and prolonged during an extremely drought-stricken year. The amplitude of variation increased with the increase in simulated precipitation. (2) After the simulated enhancement of precipitation, the start and end times of the phenology (leaf senescence and leaf fall) of N. tangutorum during the autumn advanced in an extremely wet year but was delayed during an extremely dry year, and the duration of phenology was prolonged in both extremely dry and wet years. The amplitude of variation increased with the increase in simulated precipitation. (3) The regulation mechanism of extremely dry or wet years on the spring phenology of N. tangutorum lay in the different degree of influence on the start and end times of leaf budding and leaf unfolding. However, the regulation mechanism of extremely dry or wet years on the autumn phenology of N. tangutorum lay in different reasons. Water stress caused by excessive water forced N. tangutorum to start its leaf senescence early during an extremely wet year. In contrast, the alleviation of drought stress after watering during the senescence of N. tangutorum caused a delay in the autumn phenology during an extremely dry year.

The biomass of phytoplankton, microzooplankton, copepods, and gelatinous zooplankton were measured in two tributaries of the Chesapeake Bay during the springs of consecutive dry (below average freshwater flow), wet (above average freshwater flow), and average freshwater flow years. The potential for copepod control of microzooplankton biomass in the dry and wet years was evaluated by comparing the estimated grazing rates of microzooplankton by the dominant copepod species (Acartia spp. andEurytemora affinis) to microzooplankton growth rates and by calculating the percent of daily microzooplanton standing stock removed through copepod grazing. There were significant increases in phytoplankton and copepod biomass, but not for microzooplankton biomass in the wet year as compared to the dry year. The ctenophoreMnemiopsis leidyi was present during the dry year but was absent during the sampling period of the wet and average freshwater flow years. Grazing pressure on microzooplankton was greatest in the wet year, withAcartia spp. andE. affinis ingesting 0.21–2.64 μg of microzooplankton C copepod−1 d−1 and removing up to 60% of the microzooplankton standing stock per day. In the dry year, these copepod species ingested 0.10–0.73 μg of microzooplankton C copepod−1 d−1 with a maximum daily removal of approximately 3% of the microzooplankton standing stock. Potential copepod grazing pressure was significantly less than microzooplankton growth in the dry year, but was equivalent to microzooplankton growth in the wet year, implying strong top-down control of the microzooplankton community in the wet year. These results suggest that increased grazing control of microzooplankton populations by more copepods in the wet year released top-down control of phytoplankton. Reduced microzooplankton grazing, in conjunction with increased nutrient availability, resulted in large increases in phytoplankton biomass in the wet year. Increased freshwater flow has the potential to influence trophic cascades and the partitioning of plankton production in estuarine systems.

Declining surface water quality is of great concern across the Great Plains. Recent trends in the earth’s climate can create abrupt changes in precipitation, which can alter the impact of nonpoint sources on water quality. A 2-year study [dry (2009) and wet (2010) year] was initiated to assess the impact of nitrate nitrogen (N) loss from the Roca watershed on water quality in Salt Creek. The water flow and nitrate N concentration was determined weekly in Salt Creek. The predicted average nitrate N concentration in runoff during the dry year (38.3 mg L−1) was almost five times greater than that (7.9 mg L−1) for the wet year. However, the predicted amount of nitrate N in runoff was similar for both years because the runoff for the wet year (51.8 million m3) was about five times greater than that for the dry year (10.7 million m3). The total amount of nitrate N found in Salt Creek was 18 and 127 metric tons for the dry and wet years, respectively. These data implied that 95% (dry year) and 69% (wet year) of the nitrate N has been removed from streams water in Salt Creek. Factors responsible for removing nitrate N from water include heavy growth of algae, weeds, and aquatic plants as well as denitrification and volatilization reactions. The predicted amount of nitrate N lost from soils by leaching was almost seven times greater for the wet (1,037 metric tons) than the dry year (156 metric tons). It was concluded that high precipitation for the wet year raised both the amount of nitrate N in runoff and loading into Salt Creek and could increase the negative impact on water quality.

During the 1980–1999 period, many regions in the central and southern Great Plains experienced the longest and strongest increase in average annual precipitation of the century. The size of the increase ranged from 6 to 12% of mean annual precipitation and from 25 to 60% of interannual precipitation variability. Precipitation increased for dry, average, and wet years, though not equally for each category. Generally, precipitation in very wet years increased less than in average and dry years. The probability of occurrence of dry years was greatly reduced compared to earlier in the century, whereas the probability of average years remained about the same and the probability of wet years increased. The observed decade-scale precipitation increase is attributed to a reduction in the number and severity of dry years, as well as to an increase in the number of wet years, though very wet years did not increase as much. The seasonal distribution of the increase in precipitation showed no statistically significant prevalence during any one particular month, yet qualitative considerations suggest that early summer and autumn months capture more of the annual precipitation increase. In the northern and northwestern Great Plains, a similar precipitation increase, but of smaller proportions, was observed during the 1990–1999 period.

The present study investigates the year-to-year variations of September–October rainfall in Hainan, China, for the period 1965–2010. The dominant circulation anomalies feature a cyclone (an anticyclone) over the Indochina Peninsula and northern South China Sea, an anticyclone (a cyclone) over subtropical western North Pacific and lower-level convergence (divergence) over the Maritime Continent in the wet (dry) years. These circulation anomalies are responses to an east–west sea surface temperature (SST) anomaly pattern with negative (positive) SST anomalies in the equatorial central Pacific and positive (negative) SST anomalies around the Maritime Continent in the wet (dry) years. Although the SST anomaly pattern is similar (but with opposite anomaly), the SST signal in the equatorial central Pacific is more significant in the dry years than in the wet years. This difference indicates a larger case-to-case variability in the wet years than in the dry years. The large variability in the wet years is attributed to contributions of tropical cyclones (TCs) and intraseasonal oscillations (ISOs). There are more TCs impinging on Hainan and the TC tracks are closer to the island in the wet years than in the dry years. The rainfall shows large intraseasonal variations with periods of 10–20 and 30–60 days during September–October in the wet years. The 10–20-day ISO originates from the Maritime Continent, whereas the 30–60-day ISO develops over tropical Indian Ocean and propagates northeastward to northern South China Sea. In contrast, the ISO signal is much weaker in the dry years.

Hydrological models often perform poorly in simulating dry years in regions with large inter-annual variability in rainfall. We calibrated the Soil and Water Assessment Tool (SWAT) model to dry and wet years separately, using the semi-arid Barrett watershed on the west coast of USA as an example. We used hydrological and meteorological data from 1980–2010 to calibrate the SWAT model parameters, compared the monthly runoff results simulated by SWAT using a traditional calibration for the entire runoff series with results using a calibration with the wet and dry year series, and analyzed differences in the most sensitive parameters between the wet and dry year series. The results showed that (1) the SWAT model calibrated to the entire runoff series produced significant differences in simulation efficiency between the wet years and dry years, with lower efficiency during the dry years; (2) the calibration with separate wet and dry years greatly enhanced the SWAT model’s simulation efficiency for both wet and dry years; (3) differences in hydrological conditions between wet and dry years were represented by changes in the values of the six most sensitive parameters, including baseflow recession rates, channel infiltration rates, Soil Conservation Service (SCS) curve number, soil evaporation, shallow aquifer flow, and soil water holding capacity. Future work can attempt to determine the physical processes that underlie these parameter changes and their impact on the hydrological response of the semi-arid watersheds.

Hydrological models often perform poorly in simulating dry years in regions with large inter-annual variability in rainfall. We calibrated the Soil and Water Assessment Tool (SWAT) model to dry and wet years separately, using the semi-arid Barrett watershed on the west coast of USA as an example. We used hydrological and meteorological data from 1980–2010 to calibrate the SWAT model parameters, compared the monthly runoff results simulated by SWAT using a traditional calibration for the entire runoff series with results using a calibration with the wet and dry year series, and analyzed differences in the most sensitive parameters between the wet and dry year series. The results showed that (1) the SWAT model calibrated to the entire runoff series produced significant differences in simulation efficiency between the wet years and dry years, with lower efficiency during the dry years; (2) the calibration with separate wet and dry years greatly enhanced the SWAT model’s simulation efficiency for both wet and dry years; (3) differences in hydrological conditions between wet and dry years were represented by changes in the values of the six most sensitive parameters, including baseflow recession rates, channel infiltration rates, Soil Conservation Service (SCS) curve number, soil evaporation, shallow aquifer flow, and soil water holding capacity. Future work can attempt to determine the physical processes that underlie these parameter changes and their impact on the hydrological response of the semi-arid watersheds.

Declining surface water quality is of great concern across the Great Plains. Recent changes in the earth’s climate can create abrupt changes in domestic weather that can alter the impact of nonpoint sources on water quality. A 2-year study (dry and wet years) was conducted to assess the impact of annual precipitation and runoff on water quality. Both dissolved and sediment-bound forms of alkaline earth elements (calcium (Ca), magnesium (Mg), potassium (K), barium (Ba), and strontium (Sr)) were determined weekly in runoff. Dissolved forms accounted for most of the element contents in runoff. The average concentrations of dissolved Ca, Mg, K, Ba, and Sr in runoff during the dry year (104, 24, 7.6, 0.38, and 0.61 mg/L, respectively) were greater than those during the wet year (65, 15.5, 7.2, 0.19, and 0.37 mg/L, respectively). On the contrary, the annual element loadings in surface water were greater for the wet year than those during the dry year. Calcium contributed to the greatest loadings (920 and 2,234 metric tons for the dry and wet years, respectively), whereas Ba had the least loadings at 3.7 metric tons for the dry year and 12.3 metric tons for the wet year. We concluded that greater precipitation during the wet year increased the negative impact of runoff alkaline earth elements on water quality in the Great Plains.

Climate change is intensifying the hydrologic cycle and is expected to increase the frequency of extreme wet and dry years. Beyond precipitation amount, extreme wet and dry years may differ in other ways, such as the number of precipitation events, event size, and the time between events. We assessed 1614 long-term (100year) precipitation records from around the world to identify key attributes of precipitation regimes, besides amount, that distinguish statistically extreme wet from extreme dry years. In general, in regions where mean annual precipitation (MAP) exceeded 1000mm, precipitation amounts in extreme wet and dry years differed from average years by ~40% and 30%, respectively. The magnitude of these deviations increased to >60% for dry years and to >150% for wet years in arid regions (MAP<500mm). Extreme wet years were primarily distinguished from average and extreme dry years by the presence of multiple extreme (large) daily precipitation events (events >99th percentile of all events); these occurred twice as often in extreme wet years compared to average years. In contrast, these large precipitation events were rare in extreme dry years. Less important for distinguishing extreme wet from dry years were mean event size and frequency, or the number of dry days between events. However, extreme dry years were distinguished from average years by an increase in the number of dry days between events. These precipitation regime attributes consistently differed between extreme wet and dry years across 12 major terrestrial ecoregions from around the world, from deserts to the tropics. Thus, we recommend that climate change experiments and model simulations incorporate these differences in key precipitation regime attributes, as well as amount into treatments. This will allow experiments to more realistically simulate extreme precipitation years and more accurately assess the ecological consequences.

Rivers are one of the most critical and common supplies for drinking water, agricultural, and industrial uses. The purpose of this study was to investigate the effect of land use changes on surface water quality of the Godarkhosh River as a semi-arid catchment in Iran, during dry and wet years using remote sensing, GIS and multivariate statistical techniques and compared the water quality parameters with Wilcox classification and Schuler diagram for classification of drinking water quality. Results showed that urban and barren land uses were the key factor affecting water quality variation. More minor water quality was accompanied with a more proportion of the urban and barren land uses during the wet and dry years in the catchment. No significant correlation was identified between the pH, SAR, Cl− and Ca2+ values with the land use types in both wet and dry years, whereas the EC, TDS, and Mg2+ concentrations were strongly associated with at least one land use type. A negative correlation of the most water quality parameters was obtained with grasslands and forestlands, especially in the wet year compared with other land uses. Generally, it can be concluded that the relevances between water quality parameters and land use types were stronger in the dry year than that in the wet year. Also, the correlation analysis indicated that all water quality parameters had negative relationships with the river flows. Furthermore, most of the water quality variables showed the increasing trend over time based on Mann–Kendall trend analysis. The results of this research showed that a combination of remote sensing methods, geographic information systems and multivariate statistical techniques can provide an overview of the relationship between land use and water quality and recommend that water quality can be betterment with suitable land use management.

The cyclical nature of hydrological regime of a mountain and upland river in the upper Vistula catchment in the multi-year period of 1984–2012: A potential tool for paleohydrology analysis

Simulating the effects of extreme dry and wet years on the water use of flooding-irrigated maize in a Mediterranean landplane