Climate Impacts on Water Resources | Climate Change Impacts | US EPA
But the relative impacts of different types of land use on the surface water are yet to Point and Nonpoint Sources (BASINS), was adopted to model the plausible effects of land use on climate change and land use in the United Kingdom. Sep 6, The impact of land use changes caused by urban sprawl on water and agriculture can modify the surface characteristics of watersheds that influence runoff quality and quantity . water quality at a local or regional scale for watershed management and conservation Registered in England & Wales No. characterize increasing interaction between land use and climate Over 75% of Earth's land surface has now been impacted by human help us predict future changes in water management . . Gu et al. in this issue analyzes changes in stream flow and the relationship with .. Cambridge, UK,
Warmer temperatures increase the rate of evaporation of water into the atmosphere, in effect increasing the atmosphere's capacity to "hold" water. Changes in the amount of rain falling during storms provide evidence that the water cycle is already changing. Over the past 50 years, the amount of rain falling during very heavy precipitation events has increased for most of the United States.
Furthermore, rising temperatures cause snow to begin melting earlier in the year. This alters the timing of streamflow in rivers that have their sources in mountainous areas.
Many important economic activities, like producing energy at power plants, raising livestock, and growing food cropsalso require water.
The amount of water available for these activities may be reduced as Earth warms and if competition for water resources increases. Recent droughts, reductions in winter precipitation and snow pack, and warmer, drier springs have caused water supplies in Colorado River reservoirs to decrease.
Expected climate change impacts on Colorado River water supply include: Increased year-to-year changes in water storage in reservoirs are possible, even under current conditions.
Reductions in river discharge and runoff from snowmelt. Annual snowmelt runoff could also shift to earlier in the spring. The amount of water available in these areas is already limited, and demand will continue to rise as population grows.
Many areas in the West have experienced less rain over the past 50 years, as well as increases in the severity and length of droughts; this has been especially of concern in the Southwest. This will make it more difficult for water managers to satisfy water demands throughout the course of the year. For example, in the Northeast and Midwest increases in heavy precipitation events could cause problems for the water infrastructure, as sewer systems and water treatment plants are overwhelmed by the increased volumes of water.
Heavy rain in damaged the city water system in Asheville, North Carolina. As the sea rises, saltwater moves into freshwater areas. This may force water managers to seek other sources of fresh water, or increase the need for desalination or removal of salt from the water for some coastal freshwater aquifers used as drinking water supply. Drought can cause coastal water resources to become more saline as freshwater supplies from rivers are reduced.
For example, Parsons and Gilvear illustrated the re-establishment of nature conservation corridors as landforms evolved with changes in river management.
Hoffman and Rohde used repeat landscape photography to illustrate the environmental history of an area. Hydrological processes such as evapotranspiration, interception, infiltration and percolation may change due to modifications of land cover type which can alter the water balance of a catchment Nosetto et al. The management of land use activities can play a role, e.
Studying the past allows us to place recent and ongoing changes to water quality into perspective, and to adopt a proactive rather than reactive approach to river and land management so that adaptive management can be implemented Spink et al. Although there have been several studies elsewhere e.
This is especially true where the rivers are an important water supply source for the human population, economically and for the provision of ecosystem goods and services, such as along the Southern Cape coast. Each of the sub-catchments studied has unique characteristics which influence water quality and the purpose was to analyse each one separately. The questions addressed were: The two main coastal sub-catchments, of the Touws The Touws River feeds an estuary, and the Wilderness Lakes are fed by the Duiwe and Langvleispruit Rivers with a channel connecting the lake system to the same estuary.
Climate Impacts on Water Resources
The area is ecologically sensitive and has a rich biodiversity with vegetation biomes forming part of the Cape Floral Kingdom Pauw, which include the Wilderness Lakes system, a Ramsar site protected in the Garden Route National Park Russell, Rainfall occurs throughout the year with little seasonal variation, the wettest period being from September to March and the driest being April-August.
Fynbos, the natural shrubland vegetation, has a high degree of species richness and endemism and has been descibed by Mucina and Rutherford Cathment characteristics are described in Tables 1 and 2. The historical analysis provided an initial context for water quality comparison in each catchment since water quality response to the historical pattern of land use change and catchment impacts can be immediate or have a lag effect. Digital, orthorectified aerial photographs forand were available.
The earliest photographs were orthorectified to a common scale and mosaiced using a digital elevation model as a base layer for topographical data. The same area was assessed and digitised on-screen using ArcMap The mapping boundaries used were sub-catchments delineated by Maherry et al.
The percentage for each land cover category was calculated for the sub-catchment and a buffer zone along each bank of the rivers. A buffer zone of approximately m was used based on the lowest resolution of the digital data and catchment topography.
Surface water quality, rainfall and flow data Historical water quality and flow data were used to determine how changing land cover impacted water quality data obtained from the Department of Water and Sanitation DWS, a, b.
There were two gauging stations where the river water quality has been sampled on a monthly basis. Daily and monthly flow data were also available. Statistical analysis was applied to water quality and flow data, including the non-parametric Spearmans rank correlation rs test and the seasonal Mann-Kendall trend test in XLSTAT Addinsoft. Daily rainfall data were obtained from the South African Weather Service SAWS database for 2 rainfall stations and a third was obtained from a private landowner.
Rainfall and streamflow data were analysed to detect trends as well as to clarify wet and dry years and used to determine if there were any links to water quality. A hydrological year was classified as dry 25th percentile or lesswet 75th percentile or greater or normal between the 25th and 75th percentiles Du Toit and O'Connor, To determine if there were any significant correlations spatially between water chemistry and land cover, principal component analysis PCA was performed using XLSTAT Addinsoft so that the influence of land cover data on water chemistry within the buffer area could be examined.
Exotic pine plantations cover ha in this catchment.
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The most change occurred in the lower Touws River catchment on the coastal plateau and coastal plain areas with the establishment of irrigated pastures and smallholdings. Smallholdings reached ha by but decreased by 2. Irrigated pastures increased from ha 1. Some small earth farm dams 2 ha became established with the increase in agriculture but the percentage remained small 0. As agriculture intensified, more water was required to support agricultural activities so the number of farm dams increased, from 32 ha to 53 ha 0.
The Knysna Afromontane forests increased in the Touws by and remained approximately the same in the Duiwe catchment. However, some of this increase in the Touws catchment was also due to invasions by exotic Black Wattle.
A substantial shift in agriculture occurred after with the introduction of centre pivot irrigation systems. In the Touws catchment, the Outeniqua Plateau fynbos made way for a formal low-cost housing project, Touwsranten, which was initiated in The housing project expanded to reach its current extent from 15 ha in to 31 ha in mainly occurring in the Touws River catchment.
Surface water quality, flows and rainfall The rain stations showed the same trends with very wet and very dry periods occurring in the same years, which were linked to the occurrences of floods and droughts Table 4. The coefficient of variation between the rain stations was very similar and analysis of the number of rainy days showed a decreasing trend for all stations, but the rain intensity at each station overall showed an increasing trend Fig.
The daily flow data for the Duiwe River indicated that periods of zero flows often occur.
However, the rainfall effects on the river discharge in the Duiwe River are reduced due to increased anthropogenic activities in the catchment related to dams and run-of-river abstractions. The location of the rain station that was used was also further upstream in the catchment compared to where flows were recorded in the Duiwe River. The annual runoff coefficients showed high variability throughout the years but generally increased for the Touws River and decreased for the Duiwe River Fig.
By the time flow and water quality monitoring commenced in the Duiwe catchment, agriculture was well established with grass pastures dominating the land cover. No pre-development runoff data are available for these catchments, so a dataset of mean annual runoff, which was estimated from mean annual rainfall using regional rainfall-runoff relationships developed for water resource studies see Scott et al. The Touws River accounted for more than half the runoff volume.
The gauged mean annual runoff MAR from the Touws catchment is approximately For runoff from the Duiwe catchment it was only 0. Water chemistry of the Touws River can be characterised as acidic mean pH: The Duiwe River is more alkaline mean pH: The NOx concentrations in the Duiwe River showed increased levels during or just after flood events, which were especially evident during 0. Runoff also increased during these years. In the Duiwe PO4 levels were below 0.
All major ions were significantly negatively correlated with river flows i. Drought periods also showed increases in solutes illustrated by EC concentrations in Fig. The NOx, PO4 and Si were the exception as concentrations increased with river inflows and were positively correlated to flows. Small increases coincided with very low river flow years monthly flows of Most solutes were negatively correlated to river flow with periods when concentrations for all solutes were above the TWQR thresholds.
In most cases, with the exception of NOx the Touws concentrations also exceeded those recorded in the Duiwe River. Links between land cover and surface water quality In the buffer zone riparian and adjacent land for the Touws catchment Fig. Natural Outeniqua fynbos showed a negative correlation to NOx.
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Farmers in the area made use of in-channel dams on the Duiwe River and tributaries on both the Touws and Duiwe Rivers. There is limited use of borehole water DWAF, since the quartzitic sandstones of the TMG, such as in the Touws and upper Duiwe catchments, are highly fractured and faulted, limiting the storage of groundwater Lin et l. The changing land use to pastures in the lower Duiwe catchment coupled with gentler slopes also decrease runoff Singh et al.
The rainfall data Fig. Interviews with farmers by De Lange and Mahumani indicated that the average rainfall per year mm is insufficient for optimal production of pasture areas as an average of 1 mm per year is required De Lange and Mahumani, Changes in rainfall patterns and associated evaporation rates Hoffman et al. The changing land use in the Duiwe River catchment illustrated by the extensive mapped agricultural areas and changing irrigation systems Fig.
This had a cumulative impact on water quality in the Duiwe Riverwhich also negatively impacts the lake it feeds Russell, The biophysical and chemical properties of the lakes are therefore changing since water is retained without any significant level rise Russell, Both followed the trend of increasing with increasing flows with the highest concentrations for NOx recorded at 2.
This trend was also observed by Monaghan et al. De Lange and Mahumani reported that farmers indicated increased bank erosion during high-intensity storms and floods, evidenced by siltation of their instream storage dams.
Much of the Duiwe River catchment consist of sandy topsoil that overlays clayey subsoil Table 1. Nitrogen in its soluble form NO3- is readily transported but can accumulate in soil, and phosphorus POwith its affinity to mineral surfaces, will readily attach to soil particles, especially fines such as clay Makarova et al.
This can lead to a build-up in soils on land and in farm dams so that movement will depend on remobilisation of soils by erosion Stanley and Doyle, ; Chattopadhyay et al. The pastures are covered with perennial grasses throughout the year reducing sediment loss, while vegetables with fertilizers applied are grown as row crops with limited or no vegetation stabilising sediment between them De Lange and Mahumani, The increase in nutrients in both systems after high rainfall and flow events implies that the supply may be via runoff and erosion from the land and flushing from sediments trapped by dams in the catchment.
The high density of farm dams in the Duiwe River was likely to have a cumulative impact in this regard as well as in reducing base flows, as also shown by Mantel et al.