D2 - Severe Drought. Pasture yield is limited; producers sell livestock Irrigated crops are stunted; dryland crops are brown Abundance and magnitude of wildfires may increase; fuel mitigation practices are in effect. D3 - Extreme Drought.
Livestock are suffering; producers are selling herds; feed costs are high; emergency Conservation Reserve Program CRP grazing is authorized; crop yields are low Fire danger is extreme Irrigation allotments decrease. D4 - Exceptional Drought. Federal lands begin to close for fire precautions; burn bans increase No surface water is left for agriculture; farmers use private wells Rio Grande and other large rivers are dry. Learn more about these data. Download screenshot of this panel.
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Document Date. Winter Hazards Outlook. Web Resources for New Mexico. In southern California, this shift is already happening. Between and , dominant plant species in the Santa Rosa Mountains shifted upwards in elevation by about 65 m Kelly and Goulden Warming may also affect the distribution of desert plants because of their sensitivity to freezing.
Since the lower boundary of the Sonoran desert may be where freezes never happen and the upper boundary may be where freezes last less than 24 hours, warming temperatures would allow thorny shrubs and scrub trees from further south to establish in the current boundaries of the Sonoran desert, and the Sonoran desert would expand northward, eastward, and upward in elevation Weiss and Overpeck From to , the number of days below freezing has already decreased Weiss and Overpeck Over a larger scale, these subtle impacts to plant communities may cause extensive changes, both to the distribution of whole plant communities and to individual species.
One study modeled the future distributions of vegetation in the West if unmitigated climate change continues Rehfeldt et al. The study found that over the current century, grasslands and montane forests would increase, largely at the expense of arid woodlands, and subalpine, alpine, and tundra communities.
The whole plant communities would not migrate together; instead, the range shift of each species would be unique. Of the nine species studied, Gambel oak Quercus gambelii would increase in area, and the area occupied by Douglas-fir Pseudotsuga menziesii would remain constant, but the other species, notably western larch Larix occidentalis , pinyon pine Pinus edulis , Engelmann spruce Picea engelmannii , and Utah juniper Juniperus osteosperma , would decrease drastically in area.
For example, the range of the saguaro cactus Carnegiea gigantea is projected to rise in elevation by ft and to shift northward by miles, so that its range will shift to southern Nevada. Therefore, the plant communities in these areas would have no contemporary analogue in the region, and it would be impossible to predict the exact composition and distribution of future plant assemblages over the West Rehfeldt et al.
The interaction between climate and fire may further alter vegetation communities. The effect that climate change will have on fire regimes strongly depends on the vegetation type—fires in particular vegetation types can be limited by fuel moisture or fuel availability, or both. For example, spruce-fir forests, which are relatively wet forests, naturally experience infrequent, high-severity fires, usually during drought. Therefore a shift to more arid conditions would result in more severe fires Schoennagel et al.
The fire severity in mixed conifer forests, which typically occur along a complex moisture gradient on elevations between spruce-fir forests and ponderosa pine forests, is controlled by both climate and fuel availability.
Drier conditions would result in a mosiac of fire effects on the landscape, where the fire regimes of the wetter sections of the forests would be more influenced by extended drought Schoennagel et al. Ponderosa pine forests, which are typically drier and occur at lower elevations than spruce-fir and mixed conifer forests, historically experienced frequent, low-intensity fires that were limited by the availability of fine fuels.
However, 20th century fire suppression has resulted in increased tree density; therefore, the fires that occur are high severity, stand-replacing fires Schoennagel et al. The fire regimes in pinyon-juniper woodlands are not as well studied as the fire regimes in higher elevation plant communities.
Large, stand-replacing fires in pinyon-juniper woodlands have been occurring more frequently since the s, but not enough evidence on historical fire regimes exists to determine whether this increase in large fires is due to climate Romme While the recent increased frequency of large wildfires across the West is associated with earlier spring snowmelts or spring or summer temperatures, this is not the case in the Southwest, likely because extended drought is not the only influence on severe fires in the major forest types of the region Westerling et al.
The effect that climate change will have on fire regime will also depend upon the climate variability from year to year. In the past, climate variability has influenced the outbreak of fires across the Southwest. From analyzing the fire scars in tree-ring records spread over Arizona and New Mexico, researchers have found that synchronous fires across the regions have occurred multiple times, and these fire years coincide with drought, or, in the case of open ponderosa pine forests, a wet year followed by a dry one Swetnam and Betancourt Analyses of more recent fires have uncovered the same pattern—in ponderosa pine forests, and in dry shrublands and grasslands, wet conditions in the years prior to the fire year influence the fire severity more than drought conditions in the year of the fire Littell et al.
The reason may be that during the wet years, fine fuels accumulate Swetnam and Betancourt Unlike in spruce-fir forests, fires in ponderosa pine forests and in grasslands feed off of fine fuels, like grasses and needle litter. These studies of fire history in the Southwest indicate that a warmer and drier climate may not necessarily cause more severe fires; instead the effect that climate has on individual fire regimes will depend upon the vegetation type, the overall aridity, the interannual variability of precipitation, the seasonality of the precipitation, and how the forests are managed.
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