Abstract:
Water limitations typically reduce UK wheat yields on average by 1-2 t ha-
1
,
although this can be considerably more in extreme drought years. With the
frequency and intensity of droughts expected to increase under a changing
climate, an improved understanding of the impacts of drought and better systems
for agricultural drought monitoring are required. Previous studies, however, have
found no significant relationship between UK wheat yields and commonly
employed drought severity indices (DSI). Using historical (1911-2015) daily
weather data for Cambridge the Standardized Precipitation Index (SPI), the
Standardized Precipitation and Evapotranspiration Index (SPEI), the Palmer
Drought Severity Index (PDSI) and the Potential Soil Moisture Deficit (PSMD)
were calculated on various time steps (e.g. 1-12 months for SPI and SPEI) to
provide a drought record for the site. A wheat crop growth simulation model
(Sirius) was then used to simulate the effects of the identified historic droughts
on wheat yields. The use of the Sirius crop model removed the non-drought
related yield losses (e.g. disease, pests, and lodging) present in national yield
records. Using the Spearman’s Rho correlation coefficient (r) the simulated yield
record was then correlated against the different DSIs. The droughts of 1921, 1976
and 2010 were found to be the most extreme in term of yield reduction. In
addition, there were also two noticeable periods of successive yield loss in the
early 1940s and between 2009 and 2013. All DSIs showed significant (p = 0.05)
correlations on monthly time steps between April and August. The SPI, SPEI and
PSMD showed a strong correlation to wheat yields (r = 0.64 to 0.66) on time steps
incorporating the end of the ‘construction’ and the entirety of the ‘production’
phases for wheat growth. The PDSI showed the weakest correlation (r = 0.55),
although it may be helpful in identifying yield-limiting droughts earlier in the year.
The research has contributed new scientific insights and understanding of the
impacts of historic droughts on wheat productivity, and demonstrated the
application of DSIs in monitoring potentially yield-limiting droughts. The research
also provides new evidence to support developments in UK food security and
drought management for agriculture.
