According to the Drought Monitor, drought conditions are relatively unchanged in the past two weeks. As of Feb. 12, 2013, 55.7% of the contiguous US is experiencing moderate or worse drought (D1-D4). The percentage area experiencing extreme to exceptional drought increased from 19.4% to 17.7% in the last two weeks. Percentage areas experiencing drought across the West stayed mostly the same while snowpack increased. Drought across the Southwest decreased slightly. Meanwhile, storms improved drought conditions in the Southeast.
This post precedes a significant snow event across the High and Great Plains. The NWS expects up to a foot of snow in some areas of the Plains over the next couple of days, which will provide about 1″ of liquid water equivalent. Since these areas currently suffer from a 2-4″ liquid water deficit, this storm will not break the short-term drought. Moreover, long-term drought will only be broken by substantial spring and summer rainfall. After one or two more Drought Monitor updates, we should see some welcome differences in these maps.
Figure 1 – US Drought Monitor map of drought conditions as of the 12th of February.
Figure 2 – US Drought Monitor map of drought conditions in Western US as of the 12th of February. Some small relief is evident in the past week, including some changes in the mountains as storms recently dumped snow across the region. Mountainous areas and river basins will have to wait until spring for snowmelt to significantly alleviate drought conditions.
Figure 3 – US Drought Monitor map of drought conditions in Colorado as of the 12th of February. Drought conditions held mostly steady across the state in the past week. For the first time in over a month, less than 100% of CO is experiencing Severe drought conditions. This improvement occurred over the southwestern portion of the state due to mid-season snow storms. Unfortunately, Exceptional drought conditions expanded over the northeastern plains.
Figure 4 – US Drought Monitor map of drought conditions in Southeast US as of the 12th of February. As mentioned above, drought conditions contracted a little and grew less severe in the past couple of weeks. The worst hit area, in central Georgia, has experienced the longest duration drought conditions on this map.
Cooler than normal sea-surface temperatures (SSTs) are present in the eastern Pacific, according to current MJO and ENSO data. Additionally, eastern Pacific SSTs are cooler than the climatic average due to the current negative phase of the IPO. This in turn is due in part to global warming, which is causing warmer western Pacific and Indian Ocean SSTs than usual. The cool SSTs in the eastern Pacific initiate and reinforce air circulations that generally keep precipitation away from the Southwest and Midwest US. This doesn’t mean that drought will be ever-present; only that we are potentially forcing the climate system toward more frequent drought conditions in these regions. Some years will still be wet or normal; other years (increasing in number) will be dry. This counters skeptics who claim that more CO2 and warmer temperatures are better for plants. If there is no precipitation, plants cannot take advantage of longer growing seasons. Moreover, we will experience years with increased food pressure. These conditions’ extent in the future is up to us and our climate policy (or lack thereof).
While MJO, ENSO, and IPO are all in phases that tend to deflect storm systems from the Southwest, this week’s storm demonstrates that the conditions are not ever-present. Weather variability still occurs with the dryer regime. Put another way, weather is not climate.