Türkiye’deki 2000-2015 yılları arasındaki buharlaşma ve terlemenin NOAH hidrolojik modeli ile incelenmesi
Öz
Kuraklığın incelenmesi, etkilediği alanlarda büyük zararlara sebebiyet veren bu doğal afetin niteliklerinin
(şiddet, süre, etki alanı) anlaşılması ve mümkün olan tedbirlerin araştırılması açısından çok kritiktir.
Kuraklığın gözlemlenmesinde kullanılan en önemli parametrelerden birisi olan buharlaşma ve terleme (ET)
verisidir. ET tanımı, yaş bitki ve toprakta meydana gelen buharlaşma ile kuru bitkilerde meydana gelen
terleme sonucu kaybedilen suyun toplamı olarak yapılabilir.
Su ve enerji döngüsünde önemli bir yere sahip olan ET verisi farklı metotlar kullanılarak elde
edilebilmektedir. Arazide yapılan ölçümler, hidrolojik modeller ve uzaktan algılama ile yapılan gözlemler
ET verisini elde etmek için yaygın olarak kullanılan metotlardır. Hidrolojik modeller zamansal ve mekânsal
olarak sürekli ve tutarlı veri sağladıklarından bu modellerden elde edilen ET verileri kuraklık
incelemelerinde yaygın olarak kullanılmaktadır.
Bu çalışmada, NOAH hidrolojik yeryüzü modelinden elde edilen ET değerlerinin 2000 – 2014 yılları
arasında ülkemizdeki değişimi ve ülkemizi etkisi altına alan kurak koşulların etkileri ayrıntılı bir şekilde
incelenmiştir. Yıllık olarak yapılan inceleme ile çalışma için seçilen yıllar arasında ülkemizdeki kurak ve
ıslak geçen yılların ET değerleri kullanarak belirlenmesi amaçlanmıştır. Ayrıca aylık olarak yapılan
inceleme ile 2014 yılında ülkemizde yaşanmış olan kuraklığın diğer yıllardaki ayların da kullanımı ile
belirgin bir şekilde gözlemlenmesi sağlanmıştır.
Anahtar Kelimeler
Analysis of evapotranspiration over Turkey in years between 2000 and 2015 using NOAH hydrological model
Abstract
Analysis of drought, which causes substantial
damage to affected areas, is critical in terms of
understanding this natural disaster’s characteristics
(intensity, duration, influence area) and taking
necessary precautions. Evapotranspiration (ET),
one of the most critical agricultural drought
indicators, can be retrieved using different methods.
Among them hydrological models offer a great
advantage via its potential of providing continuous
and high spatial and temporal resolution ET data.
NOAH land surface model is one of the most widely
used hydrological models to retrieve land surface
parameters and variables like soil moisture and
temperature for different layers of soil, ET, runoff,
and sensible heat. Model simulations require
availability of various atmospheric forcing data and
land surface parameters that can be obtained from
different sources at various resolutions (Table 1). In
many cases spatial resolution of the input forcing
data largely determine the spatial resolution of the
output variable.
For this study, NOAH ET simulations are obtained
at 0.25 spatial and 3 hour temporal resolution
between 2000 and 2014. Retrieved 3-hourly ET
products are later averaged into daily estimates
which are used in this study. Overall, lower ET
values over extended durations are often associated
with an ongoing agricultural drought conditions
while higher values signal wet periods.
Spatial distribution of the daily ET estimates over
entire Turkey is consistent with the expectations that
mean ET values of the Central Anatolian Region are
lower than rest of the Turkey and the coast line of
the Eastern Black Sea Region has higher mean ET
estimates and most part of the Aegean Region has
ET values with similar magnitude to the mean values
over the country.
Land surface processes over Turkey show strong
seasonal cycle: winters are wet and cold while
summers are dry and hot. As a result, day-to-day
variations of daily ET values are much higher than
inter-annual variations. This implies the retrieved
ET variability is dominated by the seasonality of this
variable. Hence, it is necessary to remove this
strong seasonality signal of land surface processes
to analyze the surface conditions. For this reason,
29-days moving window averages of ET over each
pixel are calculated separately as the seasonality of
this particular pixel (Eq. 1). Removal of these
seasonality information give the ET anomaly
information which is the primary associated with
drought.
ET anomaly time series obtained over a pixel in
Şanlıurfa – Ceylanpınar (in South Eastern region of
Turkey) is presented to give an example about the
capability of NOAH ET simulations to reflect the
local conditions. These time series show ET
anomalies in 2013 are the highest while the summer
of 2008 shows an extended duration of below
normal conditions.
Drought investigations often involve normalized
values to remove the impact of the local climate.
Accordingly, 15 year monthly averages and
standard deviations are used to normalize monthly
ET data. Such normalization helps intercomparison
of the impact of the drought over different locations
directly. Results show 2000 can be defined as most
wet year nearly all over the country. On the other
hand, 2007 and 2014 years also passed under the
influence of a dry period compared with the other
years.
The change in the severity and the areal extent of
2014 drought is monitored by analyzing the monthly
normalized ET maps between July 2013 and
September 2014 in detail over the study region.
April of 2014 is the driest April in 15 years where
drought impacted severely over large regions in
May and June 2016. The drought seemed to lose its
severity in August over most parts of the study
region.
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