In the recent climate change impact assessment on crop productivity literature,
different researchers have used different definitions of climatic variables, as Shakoor
et al. (2011) utilized simple annual average temperature and precipitation as normal
climatic parameters. Contrarily, Lobell and Field (2007) and Janjua et al. (2010)
used average of just growing season as normal climate, whereas Luo et al. (2005)
modelled integrated averages of both growing and non-growing seasons, while
Tubiello et al. (2002), Chang (2002) and You et al. (2009) employed 20 years
monthly averages of temperature and precipitation as normal climate. We modelled
20 years moving averages of the mean monthly temperature and precipitation for
wheat-growing season (November–April) as normal climatic parameters (i.e. temperature and precipitation), respectively. Normal climate variables can not only be
used as future climate predictors but also as a reference value to assess climate
anomalies (WMO 2011). Hence, we estimated the variation in both temperature and
precipitation parameters as a difference of normal temperature and precipitation
from their monthly corresponding values as proposed by Chang (2002).
Furthermore, we also modelled interaction terms of both temperature and precipitation following Ahmad and Ahmad (1998) and Ludwig et al. (2009), as they
showed that different climatic variables interact with each other and do not act
independently.
Table 2 Dependent and explanatory variables
Variables
Abbreviates Definition
Source of data
Unit of
measurement
Dependent variable
Wheat yield Y
District-wise wheat yield Pakistan Bureau of
Statistics (1984–
2013)
Tones per
hectare
Explanatory non-climatic variables
Area under
cultivation
A Wheat
District-wise per year
use of land under wheat
Pakistan Bureau of
Statistics (1984–
2013)
Thousand
hectares
Fertilizer
Fr
District-level fertilizer
data
Nation Fertilizer and
Development Center
(1984–2013)
Kg/hectare
Explanatory climatic variables
Temperature Temp.
District-wise mean
monthly temperature for
November–April
Pakistan Metrological
Department (1964–
2013)
Degree
celsius (°C)
Precipitation Precp.
District-wise mean
monthly precipitation for
November–April
Pakistan Metrological
Department (1964–
2013)
Millimetre
(mm)
Author’s own
46
M.H. Abdullah et al.
different researchers have used different definitions of climatic variables, as Shakoor
et al. (2011) utilized simple annual average temperature and precipitation as normal
climatic parameters. Contrarily, Lobell and Field (2007) and Janjua et al. (2010)
used average of just growing season as normal climate, whereas Luo et al. (2005)
modelled integrated averages of both growing and non-growing seasons, while
Tubiello et al. (2002), Chang (2002) and You et al. (2009) employed 20 years
monthly averages of temperature and precipitation as normal climate. We modelled
20 years moving averages of the mean monthly temperature and precipitation for
wheat-growing season (November–April) as normal climatic parameters (i.e. temperature and precipitation), respectively. Normal climate variables can not only be
used as future climate predictors but also as a reference value to assess climate
anomalies (WMO 2011). Hence, we estimated the variation in both temperature and
precipitation parameters as a difference of normal temperature and precipitation
from their monthly corresponding values as proposed by Chang (2002).
Furthermore, we also modelled interaction terms of both temperature and precipitation following Ahmad and Ahmad (1998) and Ludwig et al. (2009), as they
showed that different climatic variables interact with each other and do not act
independently.
Table 2 Dependent and explanatory variables
Variables
Abbreviates Definition
Source of data
Unit of
measurement
Dependent variable
Wheat yield Y
District-wise wheat yield Pakistan Bureau of
Statistics (1984–
2013)
Tones per
hectare
Explanatory non-climatic variables
Area under
cultivation
A Wheat
District-wise per year
use of land under wheat
Pakistan Bureau of
Statistics (1984–
2013)
Thousand
hectares
Fertilizer
Fr
District-level fertilizer
data
Nation Fertilizer and
Development Center
(1984–2013)
Kg/hectare
Explanatory climatic variables
Temperature Temp.
District-wise mean
monthly temperature for
November–April
Pakistan Metrological
Department (1964–
2013)
Degree
celsius (°C)
Precipitation Precp.
District-wise mean
monthly precipitation for
November–April
Pakistan Metrological
Department (1964–
2013)
Millimetre
(mm)
Author’s own
46
M.H. Abdullah et al.