Though numerous drought metrics have been developed by the research community, adoption of these metrics by water managers has been limited. The reasons for this vary, but some include mismatches in time scales and spatial scales between the metric supplied and the operational decisions (e.g. water managers often work within political boundaries, such as counties). The focus of many drought metrics is on the physical parameters with little regard to actual available water supply or societal demand. A drought in 2015 in the Pacific Northwest was unlike any other before it and caused drought advisors to seek out help with drought prediction.
One of the objectives of this study is to co-develop a metric with water managers in the Pacific Northwest to ensure that the results are useful and applicable for water management and drought declarations. Multiple discussions with the water managers led to developing a metric that is based on a measure of total moisture. Total moisture is derived from snow water equivalent and soil moisture modeled by Variable Infiltration Capacity (VIC) hydrologic model. We have developed an indicator that projects probabilistically how the year may progress based on historical patterns. This indicator enables water managers to see the probability of recovery from current drought conditions and can aid in drought declaration and water allocation.
The results of the first part of this study prompted the second part, the purpose of which is to understand the atmospheric flow and temperature patterns in spring that distinguish recovery conditions from continued dry conditions using reanalysis data. Recovery years are characterized by low geopotential height anomalies that indicate spring storms and precipitation, whereas continued dry conditions are characterized by high geopotential height anomalies that indicate reduced storm activity in the region. During years when a ridge is present over the Pacific Northwest or Eastern Pacific Ocean, optimism about spring precipitation averting an incipient drought – though historically common – is shown to be unrealistic. Understanding these relationships between geopotential height during years with low total moisture and years when total moisture recovers give insight into the drivers of these conditions.
Funding Statement (additional comments about funding)
This work was completed at the Pacific Northwest Climate Impacts Research Consortium (CIRC) and supported on grant number NA15OAR4310145 by the National Oceanic and Atmospheric Administration (NOAA) through NOAA’s Regional Integrated Sciences and Assessments (RISA) and National Integrated Drought Information System (NIDIS) programs.