Irrigation-induced Changes Research Articles

Modeling the effects of present-day irrigation on temperature extremes over China

Irrigation activities have been recognized as one of the most potentially sustainable land management practices to tackle climate change. In this study, we investigated the impacts of present-day irrigation activities on regional temperature extremes changes in China using the state-of-the-art regional climate model RegCM-4.8.2, through two sets of long-term numerical experiments (i.e., with and without irrigation). The key findings are as follows. Firstly, by comparing the observations, RegCM4 has a good ability to reproduce both the spatial distribution and the volume of irrigation for provincial irrigation activities in China. In this context, by comparing the results of numerical experiments, we found that irrigation led to significant reductions (slightly changes) in the extreme indices associated with the warm (cold) tails of the maximum and minimum temperatures distributions, e.g., hot days, tropical nights (cold nights, frost days), particularly in the regions with intense irrigation (e.g., the North China Plain). Furthermore, these extreme indices were dominated by irrigation-induced shifts in mean temperatures, but the impacts of changes in temperature variability on extreme hot events were also non-negligible for the strongly irrigated regions. In addition, through attributing irrigation-induced changes in mean state temperatures, we revealed that the irrigation-induced repartitioning of the surface turbulent heat fluxes (i.e., sensible and latent heat) dominated the variations of temperatures and the associated extremes. However, region-specific land-atmosphere coupling features also led to differences in the irrigation-induced responses of surface energy components. We highlight the possible effects and mechanisms of irrigation on multiple types of extreme temperature indices, particularly the extreme hot events, which provide scientific clues for mitigating and adapting regional climate change.

Effect of Human-Induced Land Disturbance on Subseasonal Predictability of Near-Surface Variables Using an Atmospheric General Circulation Model

Irrigation can affect climate and weather patterns from regional to global scales through the alteration of surface water and energy balances. Here, we couple a land-surface model (LSM) that includes various human land-water management activities including irrigation with an atmospheric general circulation model (AGCM) to examine the impacts of irrigation-induced land disturbance on the subseasonal predictability of near-surface variables. Results indicate that the simulated global irrigation and groundwater withdrawals (circa 2000) are ~3600 and ~370 km3/year, respectively, which are in good agreement with previous estimates from country statistics and offline–LSMs. Subseasonal predictions for boreal summers during the 1986–1995 period suggest that the spread among ensemble simulations of air temperature can be substantially reduced by using realistic land initializations considering irrigation-induced changes in soil moisture. Additionally, it is found that the subseasonal forecast skill for near-surface temperature and sea level pressure significantly improves when human-induced land disturbance is accounted for in the AGCM. These results underscore the need to incorporate irrigation into weather forecast models, such as the global forecast system.

Irrigation-Induced Changes in Chemical Composition and Quality of Seeds of Yellow Lupine (Lupinus luteus L.).

The quality and amount of yellow lupine yield depend on water availability. Water scarcity negatively affects germination, flowering, and pod formation, and thus introduction of an artificial irrigation system is needed. The aim of this study was to evaluate the influence of irrigation on the quality of yellow lupine seeds. Raining was applied with a semi-solid device with sprinklers during periods of greatest water demand. It was shown that watered plants produced seeds of lesser quality, having smaller size and weight. To find out why seeds of irrigated plants were of poor quality, interdisciplinary research at the cellular level was carried out. DNA cytophotometry evidenced the presence of nuclei with lower polyploidy in the apical zone of mature seeds. This may lead to formation of smaller cells and reduce depositing of storage materials. The electrophoretic and Fourier transform infrared spectroscopic analyses revealed differences in protein and cuticular wax profiles, while scanning electron microscopy and energy dispersive spectroscopy revealed, among various chemical elements, decreased calcium content in one of seed zones (near plumule). Seeds from irrigated plants showed slightly higher germination dynamics but growth rate of seedlings was slightly lower. The studies showed that irrigation of lupine affected seed features and their chemical composition, an ability to germination and seedlings growth.

Irrigation-Induced Changes in Evapotranspiration Demand of Awati Irrigation District, Northwest China: Weakening the Effects of Water Saving?

The evapotranspiration demand of the Awati irrigation district has changed with irrigation development since 1980. During the first period of traditional irrigation expansion from 1980 to 1997, reference crop evapotranspiration (ET0) decreased as irrigation intensity increased. Since the second period of water-saving irrigation extension began in 1998, the gross irrigation quota has decreased as the water use efficiency improved, whereas ET0 has been increasing accordingly. The increasing evapotranspiration demand has enlarged the irrigation water requirement per unit area, which partly weakens the effects of water-saving irrigation. Findings show that irrigation-induced changes in evapotranspiration demand should be considered when evaluating the performance of water-saving technologies in irrigation districts in arid areas.

Human-induced modifications to land surface fluxes and their implications on water management under past and future climate change conditions

We used a coupled land-atmospheric simulation framework to quantify the feedback impacts of water resources in a changing climate. The simulations dynamically downscaled data from the North American Regional Reanalysis (NARR) data, Climate Forecast System (CFS) Version 2 and the North American Regional Climate Change Assessment Program (NARCCAP), to investigate irrigation effects on temperatures and surface fluxes under current and future scenarios in Southern Idaho. This study implements irrigation schemes within the Noah Land Surface Model (LSM) coupled with the Weather Research and Forecast (WRF) 3.4 at a 4-km resolution to diagnose irrigation-induced changes to surface energy fluxes and boundary layer properties. Our results suggest that induced cooling via evaporation causes a decrease of 0.8°C to the air temperature over April − October, a decrease of up to 90m of the planetary boundary layer depth and an increase of 2.0°C in the dew point over the irrigated areas. On average, the growing season start date trends 0.46days/year earlier and the growing season termination date trends 0.60days/year later. A decrease in precipitation with time is also seen at all elevation ranges from the year 2040–2070, with the lowest elevation levels seeing a bigger decrease than the higher levels. Thus, irrigation-induced increases in growing degree days and modifications to surface fluxes are shown in the basin and it is critical to consider when planning both crop and water management.

Effect of Differential Irrigation on Accumulation of Canopy Temperature-Based Heat Units in Cotton

Agricultural management decisions are often timed on the basis of accumulated air temperature heat units (AT-heat unit) to coincide with crop growth and development. The relationship between AT-heat unit accumulation and crop development is affected by water deficits that alter the relationship between air and plant canopy temperature. Improved technology for monitoring canopy temperatures makes it possible to continuously monitor canopy temperature in production settings. The utility of cotton canopy temperature heat units (CT-heat unit) was assessed by comparing decadal (2000-2009) AT-heat unit variation with variation in CT-heat unit accumulation due to variable irrigation in 2009. Irrigation-induced variation in CT-heat units (1198-1416) was similar to the decadal variation in AT-heat units (1270-1508). Two heat unit-based management tools: 1) the assignment of irrigation crop coefficients and 2) the identification of a fiber thickening period were both found to be sensitive to irrigation-induced changes in CT-heat unit accumulation. The inclusion of CT-heat units resulted in variability in both indicators that reflected effects of irrigation and climate on plant performance. Inclusion of canopy temperature measurements in heat unit accumulation might improve the utility of heat units.

Water Requirement with Irrigation Expansion in Jingtai Irrigation District, Northwest China: The Need to Consider Irrigation-Induced Local Changes in Evapotranspiration Demand

Because water diverted from the Yellow River has been used for irrigation in 1972, obvious changes in evapotranspiration demand (denoted by reference evapotranspiration) have been observed in the Jingtai Irrigation District, Northwest China. Increasing irrigation-water consumption corresponding to irrigation expansion led to less local evapotranspiration demand after 1972. The crop and irrigation-water requirements per unit area were influenced by the changes in evapotranspiration demand. A simple prediction approach based on the complementary relationship of evapotranspiration was used to estimate the irrigation-induced changes in evapotranspiration demand and their influences on irrigation-water requirement. Future variations in net irrigation requirement per unit area under different irrigation scenarios at 50% and 75% precipitation levels were evaluated. Irrigation requirements per unit area would decrease under irrigation-expansion scenarios but increase under irrigation-reduction scenarios corresponding to the irrigation-induced changes in evapotranspiration demand. Irrigation-induced local changes in evapotranspiration demand should be seriously considered for irrigation planning and management.

Effects of Drip Irrigation Configuration and Rate on Yield and Fruit Quality of Young Highbush Blueberry Plants

A 4-year study was conducted to establish the effects of drip irrigation configuration and rate on fruit yield and quality of young highbush blueberry plants (Vaccinium corymbosum L. ‘Duke’). Plants were grown in a silt loam soil on raised beds and were non-irrigated or irrigated using either one or two lines of suspended drip tape. Each line configuration had in-line emitters spaced every 0.3 or 0.45 m for a total of four drip configurations. Water was applied by each drip configuration at two rates, a moderate rate of 5 L/plant per irrigation event, and a heavy rate of 10 L/plant. The frequency of irrigation was guided by measurements of soil matric potential. Irrigation was applied each year, and plants were cropped beginning the second year after planting. Rainfall was above normal in the first 2 years of the study, and differences in soil moisture were most evident in the last 2 years, in which soil matric potential increased with irrigation volume. Neither the number of irrigation lines nor emitter spacing had an effect on yield or fruit quality. Yield was unaffected by irrigation rate until the fourth year after planting and was only higher when 5 L/plant was applied. The yield increase was the result of differences in fruit weight during the second of two harvests and was associated with delays in fruit maturation. Irrigation affected plant mineral concentrations but leaves and berries responded differently; affected minerals tended to decrease in leaves but increase in the fruit. Many irrigation-induced changes in fruit quality were evident 1 or 2 years before changes in yield. Higher irrigation volume increased fruit size and water content but reduced fruit firmness and soluble solids. Irrigation reduced fruit water loss during storage and thereby promoted longer shelf life. Irrigation also resulted in a change in anthocyanin composition in the fruit but did not affect antioxidants or total anthocyanin content.

Irrigation-Induced Changes in Phosphorus Fractions of Caribou Sandy Loam Soil Under Different Potato Cropping Systems

Sequential fractionation is a common method used in eval­ uating the impacts of soil management practices on soil phosphorus (P) distribution. However, to our knowledge, this method has not been used in investigating the effects of irrigation on the changes in soil P fractions. In this work, we measured sequentially extracted P by deionized H20, 0.5 M sodium bicarbonate (pH 8.5), 0.1 M sodium hydroxide (NaOH), and 1 M hydrochloric acid (HCI) in Caribou sandy loam soil samples from 10 potato fields under different 3-year crop rotations both with and without irrigation. As inorganic fertilizer was applied to these fields, irrigation and rotation management practices mainly affected the dis­ tribution of inorganic P fractions, but had no significant changes of organic P fractions. The impact of crop rotation was mainly reflected by H20-extractable P Irrigation had greater influence on stable or re­ calcitrant P in NaOH, HCI, and residual fractions. Higher levels of NaOH-extractable inorganic P were observed in soil from rainfed fields, whereas higher levels of HCI-extractable P were observed in soils under irrigated management. Our data indicate that irrigation may eventually decrease P availability and runoff potential in these potato soils over the long term because of the partial transfer of P in the sink from the active NaOH fraction to more stable HCI and residual fractions. Whereas in­ formation and knowledge derived from this study may shed some light on the transformation mechanism of soil P fractions for sustainable agri­ cultural production, more field data from shortand long-term experiments are needed to confirm our observations.

Irrigation of steppe soils in the south of Russia: Problems and solutions (Analysis of Irrigation Practices in 1950–1990)

Experience in irrigation of chernozems in the steppe zone of Russia for a period from 1950 to 1990 is analyzed. By the end of this period and in the subsequent years, the areas under irrigation reduced considerably, and the soil productivity worsened. This was caused by the improper design of irrigation systems, on the one hand, and by the low tolerance of chernozems toward increased moistening upon irrigation, on the other hand. The analysis of the factors and regimes of soil formation under irrigation conditions shows that irrigation-induced changes in the soil hydrology also lead to changes in the soil physicochemical, biochemical, and other properties. In particular, changes in the composition of exchangeable cations lead to the development of solonetzic process. In many areas, irrigation of chernozems was accompanied by the appearance of solonetzic, vertic, saline, and eroded soils. The development of soil degradation processes is described. In general, the deterioration of irrigated chernozems was related to the absence of adequate experience in irrigation of steppe soils, unskilled personnel, improper regime of irrigation, and excessively high rates of watering. In some cases, the poor quality of irrigation water resulted in the development of soil salinization and alkalization. To improve the situation, the training of personnel is necessary; the strategy of continuous irrigation should be replaced by the strategy of supplementary irrigation in the critical periods of crop development.

Changes in soil properties at different levels of soil structural arrangement under the impact of irrigation

Processes taking place at different levels of the soil structural arrangement in irrigated and rainfed soils of the Lower Volga region are analyzed. Interactions between these processes and the dependence of their rates on the duration of irrigation are discussed. It is shown that irrigation-induced changes are more pronounced and proceed faster in soils of poorly drained landscapes in comparison with well-drained landscapes. Interaction of the processes taking place at different hierarchical levels of soil arrangement is observed. At the ionic-molecular level, migration and transformation of the composition of soil humus and soluble salts and various exchange reactions take place; at the level of elementary soil particles, the processes of disintegration, peptization, transformation, and the destruction of minerals; at the aggregate level, changes in the water stability of soil aggregates and the degree of soil micro- and macroaggregation; at the level of particular morphological elements, horizons, and pedons, reorganization of soil material (changes in the thickness and bulk density of soil horizons, synthesis and destruction of various neoformations, etc.); finally, at the level of the soil cover pattern, irrigation leads to a higher complexity of the soil cover; the degree of contrast in the soil cover pattern increases, and the soil development at different sites proceeds with different velocities.

Irrigation cooling effect on temperature and heat index extremes

Previous studies of the long‐term climate effects of irrigation have focused on average monthly temperatures. Given the importance of temperature (T) extremes to agriculture and human health, we evaluated irrigation induced changes in various metrics of T extremes using daily observations in California and Nebraska. In addition, simulations from a regional climate model were used to evaluate irrigation effects on T and heat index (HI; also known as the discomfort index) extremes in California, with the latter representing a combined measure of T and humidity. Contrary to our expectation that irrigation would have larger effects on hot days when sensible heat fluxes are higher, both observations and a regional climate model indicate that irrigation cools T on the hottest days of the year by a similar magnitude as on an average summer day. The HI is also reduced by irrigation, but by a much smaller magnitude than T because of the higher humidity above irrigated surfaces. Interestingly, HI is influenced less on the most extreme days than on average days, because of the nonlinear effect of humidity on HI at high T.

Relationships between topographically expressed zones of flow accumulation and sites of fault intersection: analysis by means of digital terrain modelling

Topographically expressed zones of flow accumulation often coincide with fault intersections because of increased rock fracturing. We have conducted a study of the interrelationships between topographically expressed accumulation zones and fault intersections, and the function of these sites in landscape evolution. The investigation has been performed with the use of digital terrain models, geological and soil data for the Crimean Peninsula. First, we carried out an analysis of associations of sites of fault intersections, intensive rock fracturing and abnormally high discharges of springs and boreholes, relating to fault intersections, with three types of landform element (zones of flow accumulation, transit and dissipation). We found that all phenomena under study are closely associated with topographically expressed accumulation zones. This has demonstrated that, within these zones, the soil moisture is influenced both by upward transport of deep-seated groundwater and by accumulation of overland lateral flows. Second, we predicted the effect of topography on irrigation-induced changes in the salt regime of soils and the groundwater level, assuming that topographically expressed accumulation zones can be marked by properties of fault intersections. We found that water leaking out of the North Crimean Canal can result in secondary salinisation of soils and a considerable rise of the watertable within some accumulation zones located downslope. Salts collected in the accumulation zones, and their slow movement through rock fractures, can lead to salinisation of the aquifers. We believe that topographically expressed accumulation zones are areas of contact and substance exchange between overland lateral and deep flows.