HOW WET CAN IT GET? DEFINING FUTURE CLIMATE EXTREMES BASED ON LATE HOLOCENE LAKE-LEVEL RECORDS

In the western U.S. many of the basins that underwent substantial lake-level fluctuations during the late Pleistocene also underwent significant fluctuations during the late Holocene and into the historical period. Here, we compare the magnitude of maximum late Holocene highstands (LHHs) in the Pyramid, Carson Sink, Walker, Mono, Tulare, and Owens lake basins to the magnitude of their historical highstands (HHs), which provides a measure of just how wet it can get in these basins under current and future climate boundary conditions that have been in place since the middle Holocene.

Table 1. Comparison of HHs and LHHs.
	HHs			LHHs
Lake	Elev. (m)	Area (km^2)	Vol. (km^3)	Elev. (m)	Area (km^2)	Vol. (km^3)	Age (cal yr BP)
Pyramid	1180	824	42	1195	908	57	~2800
Carson Sink	1185.6	1289.7	5.6	1204	3173	47.1	~850
Walker	1250	304	12.8	1262	350	16	~3700
Mono	1959	224	5.6	1980	295	11.5	~3700
Owens	1096	285	2.7	1108	336	6.5	~3700
Tulare	66	1862	9.9	68	2366	14.1	~300

During their LHHs, all of these lakes significantly increased their lake-surface elevations, surface areas, and volumes over their HHs (Table 1). Three of these lakes reached their LHHs during the neopluvial (~3700 cal yr BP), while the other three reached their LHHs during other discrete pluvials. Multiple events, however, are recorded in each basin during the late Holocene. The largest response occurred in the Carson Sink (CS) during the Medieval pluvial (MP) (~850 cal yr BP) when lake surface rose by ~20 m, surface area increased by ~240%, and volume increased by ~840%. The CS has the largest drainage basin in our sample and the Walker River may have been diverted into the CS during the MP, which may help explain this response. In addition, during the 46-year long MP, the wettest part of the Great Basin was in the headwaters of the Humboldt River, the largest tributary to the CS, which is clearly expressed in the gridded tree ring chronologies contained within the Living Blended Drought Atlas of Cook et al. (2010). The spatial-temporal variability expressed by the different timing of LHHs is probably a function of the regional variability in climate during each of these periods. Regardless of exactly when a particular basin reached its LHH, these elevated shorelines represent a measure of just how wet it can get in each basin under current and likely future climate boundary conditions.