Query: ‘The dry periods are drier and the wet periods are wetter,’ said Jeffrey Mount, a water expert and senior fellow at the Public Policy Institute of California.

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Water cycle <=SEP=> The water cycle , also known as the hydrological cycle or the hydrologic cycle , describes the continuous movement of water on , above and below the surface of the Earth . The mass of water on Earth remains fairly constant over time but the partitioning of the water into the major reservoirs of ice , fresh water , saline water and atmospheric water is variable depending on a wide range of climatic variables . The water moves from one reservoir to another , such as from river to ocean , or from the ocean to the atmosphere , by the physical processes of evaporation , condensation , precipitation , infiltration , surface runoff , and subsurface flow . In doing so , the water goes through different forms : liquid , solid ( ice ) and vapor .   The water cycle involves the exchange of energy , which leads to temperature changes . For instance , when water evaporates , it takes up energy from its surroundings and cools the environment . When it condenses , it releases energy and warms the environment . These heat exchanges influence climate .   The evaporative phase of the cycle purifies water which then replenishes the land with freshwater . The flow of liquid water and ice transports minerals across the globe . It is also involved in reshaping the geological features of the Earth , through processes including erosion and sedimentation . The water cycle is also essential for the maintenance of most life and ecosystems on the planet .

Wetland <=SEP=> A wetland is a land area that is saturated with water , either permanently or seasonally , such that it takes on the characteristics of a distinct ecosystem . The primary factor that distinguishes wetlands from other land forms or water bodies is the characteristic vegetation of aquatic plants , adapted to the unique hydric soil . Wetlands play a number of roles in the environment , principally water purification , flood control , carbon sink and shoreline stability . Wetlands are also considered the most biologically diverse of all ecosystems , serving as home to a wide range of plant and animal life .   Wetlands occur naturally on every continent except Antarctica , the largest including the Amazon River basin , the West Siberian Plain , and the Pantanal in South America . The water found in wetlands can be freshwater , brackish , or saltwater . The main wetland types include swamps , marshes , bogs , and fens ; and sub-types include mangrove , carr , pocosin , and varzea .   The UN Millennium Ecosystem Assessment determined that environmental degradation is more prominent within wetland systems than any other ecosystem on Earth . International conservation efforts are being used in conjunction with the development of rapid assessment tools to inform people about wetland issues .   Constructed wetlands can be used to treat municipal and industrial wastewater as well as stormwater runoff . They may also play a role in water-sensitive urban design .

Effects of global warming <=SEP=> The effects of global warming are the environmental and social changes caused ( directly or indirectly ) by human emissions of greenhouse gases . There is a scientific consensus that climate change is occurring , and that human activities are the primary driver . Many impacts of climate change have already been observed , including glacier retreat , changes in the timing of seasonal events ( e.g. , earlier flowering of plants ) , and changes in agricultural productivity .   Future effects of climate change will vary depending on climate change policies and social development . The two main policies to address climate change are reducing human greenhouse gas emissions ( climate change mitigation ) and adapting to the impacts of climate change . Geoengineering is another policy option .   Near-term climate change policies could significantly affect long-term climate change impacts . Stringent mitigation policies might be able to limit global warming ( in 2100 ) to around 2 ° C or below , relative to pre-industrial levels . Without mitigation , increased energy demand and extensive use of fossil fuels might lead to global warming of around 4 ° C. Higher magnitudes of global warming would be more difficult to adapt to , and would increase the risk of negative impacts .

Physical impacts of climate change <=SEP=> This article is about the physical impacts of climate change . For some of these physical impacts , their effect on social and economic systems are also described .   This article refers to reports produced by the IPCC . In their usage , `` climate change '' refers to a change in the state of the climate that can be identified by changes in the mean and/or variability of its properties , and that persists for extended periods , typically decades or longer ( IPCC , 2007d :30 ) . The climate change referred to may be due to natural causes and/or the result of human activity .

Kalahari Desert <=SEP=> The Kalahari Desert is a large semi-arid sandy savannah in Southern Africa extending 900000 km2 , covering much of Botswana , parts of Namibia , and regions of South Africa .