Development of data-driven statistical models for daily water table depth prediction and variable selection: Two case studies in coastal plain forested wetlands

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

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

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.

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.

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.

The transition zones (ecotone) between boreal forests and peatlands: Modelling water table along a transition zone between upland black spruce forest and poor forested fen in central Saskatchewan

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

Abstract. Drainage in tropical peatlands increases CO2 emissions, the rate of subsidence, and the risk of forest fires. To a certain extent, these effects can be mitigated by raising the water table depth (WTD) using canal or ditch blocks. The performance of canal blocks in raising WTD is, however, poorly understood because the WTD monitoring data are limited and spatially concentrated around canals and canal blocks. This raises the following question: how effective are canal blocks in raising the WTD over large areas? In this work, we composed a process-based hydrological model to assess the peatland restoration performance of 168 canal blocks in a 22 000 ha peatland area in Sumatra, Indonesia. We simulated daily WTD over 1 year using an existing canal block setup and compared it to the situation without blocks. The study was performed across two contrasting weather scenarios representing dry (1997) and wet (2013) years. Our simulations revealed that, while canal blocks had a net positive impact on WTD rise, they lowered WTD in some areas, and the extent of their effect over 1 year was limited to a distance of about 600 m around the canals. We also show that canal blocks are most effective in peatlands with high hydraulic conductivity. Averaging over all modeled scenarios, blocks raised the annual mean WTD by only 1.5 cm. This value was similar in the dry (1.44 cm) and wet (1.57 cm) years, and there was a 2.13 fold difference between the scenarios with large and small hydraulic conductivities (2.05 cm versus 0.96 cm). Using a linear relationship between WTD and CO2 emissions, we estimated that, averaging over peat hydraulic properties, canal blocks prevented the emission of 1.07 Mg ha−1 CO2 in the dry year and 1.17 Mg ha−1 CO2 in the wet year. We believe that the modeling tools developed in this work could be adopted by local stakeholders aiming at a more effective and evidence-based approach to canal-block-based peatland restoration.

The objective of this study was to obtain physiological information for the increasing yield of soybeans at drained paddy fields by controlling the water table level. We studied the effects of various water table levels using lysimeter (15cm∼100cm constant, fluctuation, no-irrigation) on leaf chlorophyll content, root growth and yield of soybeans grown on alluvial soil, which is a major soil type in the soybean producing area in Japan. Experiments were carried out in 1991 (wet year) and 1992 (dry year) at Tsukuba (1991, 1992) and Fukuyama (1992). Effects of water table on chlorophyll contents varied with leaf position on the main stem. The lower leaves contained more chlorophyll when the plants were grown at lower water table. The upper leaves responded in the same way as lower leaves in wet year, whereas the chlorophyll content was highest at a 40cm depth in dry year. The root length densities in each soil layer were also affected by water table : two peaks of root length density (upper layer and just above the water table) were observed in the 7Ocm-depth treatment, whereas the peak was observed only at the uppermost layer in the 20cm or 40cm depth treated plots. The effects of water table on yield seem to be affected by the amount of rainfall. The highest yield was brought in by 70cm-depth water table treatment in wet year, and by 40cm in dry year. Fluctuation of water table reduced yield. The results indicate that for getting a higher yield of soybeans at drained paddy field, it is important to maintain water table at a suitable level, which should be adjusted according to rainfall.

WRF model coupled to water table dynamics has been adapted to investigate the spatial and temporal evolution of wet and dry conditions over Lake Victoria Basin. Two 2‐year long simulations were conducted using coupled model with water table and the uncoupled (without water table) for wet and dry periods. Influence of water table on land–atmosphere coupling and interconnections among precipitation, soil moisture, evapotranspiration, and surface energy fluxes were examined. Overall, the coupled model simulated significantly higher monthly rainfall amounts during both the short (March‐May) and long (October‐December) rains of the wet year, which was more consistent with observations particularly over the lake surface and immediate hinterlands. Simulated monthly rainfall differences between coupled and uncoupled were pronounced during the peak of long rains, exceeding 100mm over the lake surface. Toward the end of the rainfall season (May) the difference was minimal. During the short rains significant differences occurred mostly in November, especially over the eastern shores. But during the relatively dry year minimal differences were generally witnessed throughout the year except in May, east of Lake Victoria. The coupled model simulated stronger matching among rainfall, soil moisture, and evapotranspiration over areas with shallow water table, for example in Kisumu to the east and Bukoba to the west. In these areas coupled model simulated higher soil moisture corresponding to higher evapotranspiration and precipitation. These interconnections were more pronounced during short and long rains in 1997 (wet) compared to 2010 (dry). Wet conditions over the gulf of Kisumu corresponded with rise in water table especially during October–December 1997 consistent with ENSO‐related flooding over the area. Hence, our study demonstrated that incorporating water table resulted in realistic interconnections between precipitation, soil moisture, ET, and surface energy fluxes, and could improve simulation and prediction of spatial‐temporal evolution of wet and dry conditions over Lake Victoria Basin.

Experiments were conducted during the winter seasons of 1983–1984 and 1984–1985 to identify suitable irrigation regimes s for wheat grown after rice in soils with naturally fluctuating shallow water table (SWT) at a depth of 0.4 to 0.9 m and medium water table (MWT) at a depth of 0.8 to 1.3 m. Based on physiological stages, the crop was subjected to six irrigation regimes viz., rainfed (I0); irrigation only at crown root initiation (I1); at only crown root initiation and milk (I2); at crown root initiation, maximum tillering and milk (I3); at crown root initiation, maximum tillering, flowering and milk (I4); and at crown root initiation, maximum tillering, flowering milk and dough (I5). Tube-well water with an EC <0.4 dsm−1 was used for irrigation. Based on 166 mm effective precipitation during the cropping season, 1983–1984 was designated as a wet year and 1984–1985 with 51 mm as a dry year. The change in profile soil water content ΔW (depletion) in the wet year was less (23%) under SWT and 10% under MWT as compared to the dry year. The ground water contribution (GWC) to evapotranspiration (ET) was 58% under SWT and 42% under MWT conditions in both the years. The GWC in the wet year was 20% under SWT and 23% under MWT. Of the total net water use (NWU), about 85% was ET and 15% drainage losses. The NWU was highest (641 and 586 mm) in I5 under SWT and MWT conditions, respectively, but not the yield (5069 kg ha−1). Compared to I5, NWU in I2 treatment decreased by 10% in the wet and 25% in the dry year. A similar trend was observed in the I3 treatment under MWT condition. However, there was no statistically significant difference between yields of the I1 to I5 treatments of either water table depth during the wet year. This was also true during the dry year for the I2 to I5 treatments. Under SWT, in I2, the grain yield was 5130 kg ha−1 and under I3 regime, 5200 kg ha−1. Under MWT in I3, the yield was 5188 kg ha−1 and under I4 regime, 5218 kg ha−1. Thus it appears that in the Tarai region where the water table remains shallow (<0.9 m) and medium (<1.3 m) for most of the wheat growing season applications of more than 120 and 180 mm irrigation under SWT and MWT conditions, respectively were not necessary. Irrigation given only at crown root initiation and milk stages under shallow water table conditions, and at crown root initiation, maximum tillering and milk stages under medium water table conditions, appears to be as effective as frequent irrigations.

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.