Agricultural Ecosystem

Agricultural Ecosystems

Men and women rice farmers working in Nepal.
Credit: B. Sthapit/Bioversity

Managing genetic resources on farms concerns the entire ecosystem, including cultivated crops, forages and agroforestry species, as well as their wild and weedy relatives that may be growing in nearby areas.There are many benefits from effective on farm genetic resources management programmes.

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Conserving the processes of evolution and adaptation
Conserving and using diversity at different levels
Integrating farmers into a national plant genetic resources system
Improving the livelihoods of resource-poor farmers
Maintaining or increasing farmers’ control and access over genetic resources
Managing stress and change
Seed systems and diversity maintenance
Ecosystem services
Linking wild and cultivated systems

Conserving the processes of evolution and adaptation
The conservation and use of agrobiodiversity at all levels within local environments helps ensure that the ongoing processes of evolution and adaptation of crops to their environments are maintained within farming systems. This benefit is central to in situ management of genetic resources, as it is based on conserving and using not only existing germplasm but also the conditions that allow for the development of new germplasm.

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Heat Island

An urban heat island (UHI) is a metropolitan area which is significantly warmer than its surroundings. The temperature difference usually is larger at night than during the day and larger in winter than in summer, and is most apparent when winds are weak. The main cause of the urban heat island is modification of the land surface by urban development; waste heat generated by energy usage is a secondary contributor. As population centres grow they tend to modify a greater and greater area of land and have a corresponding increase in average temperature. Partly as a result of the urban heat island effect, monthly rainfall is about 28% greater between 20-40 miles downwind of cities, compared with upwind Causes

here are several causes of a UHI, as outlined in Oke (1982). The principal reason for the night-time warming is (comparatively warm) buildings blocking the view to the (relatively cold) night sky (see thermal radiation). Two other reasons are changes in the thermal properties of surface materials and lack of evapotranspiration in urban areas. Materials commonly used in urban areas, such as concrete and asphalt, have significantly different thermal bulk properties (including heat capacity and thermal conductivity) and surface radiative properties (albedo and emissivity) than the surrounding rural areas. This causes a change in the energy balance of the urban area, often leading to higher temperatures than surrounding rural areas. The energy balance is also affected by the lack of vegetation in urban areas, which inhibits cooling by evapotranspiration.

Other causes of a UHI are due to geometric effects. The tall buildings within many urban areas provide multiple surfaces for the reflection and absorption of sunlight, increasing the efficiency with which urban areas are heated. This is called the “canyon effect“. Another effect of buildings is the blocking of wind, which also inhibits cooling by convection. Waste heat from air conditioning, industry, and other sources also contributes to the UHI. High levels of pollution in urban areas can also increase the UHI, as many forms of pollution change the radiative properties of the atmosphere.

Effects of Global Warming

How Will Global Warming Impact California?

IPCC Emissions Scenarios		Summary of Projected Global Warming Impacts (2070-2099, as compared to 1961-1990)	State-wide Temp-erature Rise
Higher Emissions: Rapid, fossil-fuel intensive growth		90% loss in Sierra snow pack 22-30 inches of sea level rise 3-4 times as many heatwave days in major urban centers 2.5 times the number critically dry years 4-6 times as many heat-related deaths in major urban centers 20% increase in electricity demand Increase in days meteorologiclaly conducive to ozone formation	Higher Warming Range: 8-10.4 ºF
Medium-High Emissions: Primarily fossil-fuel dependent growth with some green technology		70- 80 % loss in Sierra snow pack 14-22 inches of sea level rise 2.5-4 times as many heatwave days in major urban centers 2-6 times as many heat-related deaths for major urban centers 75-85% increase in days meteorologically conducive to ozone formation 2-2.5 times the number critically dry years 11% increase in electricity demand 30% decrease in forest yields (pine) 55% increase in the expected risk of large wildfires	Medium Warming Range: 5.5- 7.9 ºF
Lower Emissions: Shift to service & information economy with lots of green technology		30-60 % loss in Sierra snow pack 6-14 inches of sea level rise 2-2.5 times as many heatwave days in major urban centers 2-3 times as many heat-related deaths for major urban centers 25-35% increase in days meteorologically conducive to ozone formation Up to 1-1.5 times the number critically dry years 3-6 % increase in electricity demand 7-14% decrease in forest yields (pine) 10-35% increase in the risk of large wildfires	Lower Warming Range: 3.0-5.4 ºF

Source: Cayan, D., Luers, A., Hanemann,M. , Franco, G. and Croes, B. 2006. Climate Change Scenarios for California: an Overview. California Energy Commission PIER working paper.