2.2 Data sources and quality control
Daily meteorological dataset of five parameters including mean
temperatures (°C), rainfall (mm), relative humidity (%), wind speed (km
day−1), and sunshine (h day−1) were
obtained from the Bangladesh Meteorological Department (BMD). Though BMD
has 43 weather stations throughout the country, the majority of the
stations are unevenly distributed, some of them are newly equipped and
few stations have no longer datasets. In this study, we used 18 weather
stations dataset that measures meteorological parameters essential for
calculating ETref (Fig. 1). The problem arises when missing data exist.
If the missing data was observed in any year >2%, the data
of that particular year was omitted. When the data comprised of
>2% missing values (Rubin et al., 2007), the supplied
estimated data might have inaccurate, subsequently inaccurate outputs
may provide. Rahman and Islam (2019) also employed the threshold level
for showing missing precipitation in Bangladesh. Other studies applied
to the threshold of 2% for data quality control purposes (Vieira,
2017). After initial scrutiny, the availability of weather datasets at
various sites was observed to range between 30 to 48 years. We used 37
years of daily climatic records during 1980–2017. It is noted that for
a good representation of the data stations were selected which are
uniformly scattered all over the
country. However, quality control
of the dataset was primarily undertaken thoroughly by checking namely,
positive values of parameters, for example, Tmin is lower than Tmax, and
humidity is less than 100%. Time series and homogeneity tests of the
dataset were conducted to exhibit any anomaly in the dataset (Islam et
al. 2020b). Besides, the quality appraisal of the dataset of the
selected stations was performed using a subjective double mass curve
procedure and the objective Standard Normal Homogeneity Test (SNHT)
(Fig. S1). Each dataset was detected consistently to fit for
quantitative appraisal. The SNHT and K-S tests among various subsets of
datasets depicted no significant difference in those datasets for all
the parameters at the 95% confidence level (Table S1). Hence, the
quality of the datasets was achieved suitable for further appraisal.