İklim Değişikliğinin Buğday Bitkisinin Gelişimi Ve Verimine Olası Etkilerinin Bitki-iklim Simulasyon Modeli İle İncelenmesi

Abstract

İklim değişikliği günümüzde Dünya genelinde hemen herkesin hem fikir olduğu, ancak olası etkileri hakkında sıkça tartışmaların yaşanadığı ve birçok araştırmanın ana hedefi olmuş ciddi bir konudur. Hükümetler arası iklim değişimi organizasyonu (IPCC) raporlarına göre, çeşitli kaynaklardan doğaya salının sera gazlarındaki artış, küresel ortalama sıcaklığını etkilemektedir. Bu durum dünya iklimini makro, mezo ve mikro ölçekte değiştirmektedir ve değiştirecektir. Tarımsal üretimin planlanması ve gelecekteki durumunun belirlenmesi geçmişten günümüze insan hayatında büyük önem arz etmektedir. Toprak, bitki ve atmosfer arasındaki etkileşim, tarımsal üretime yön veren en önemli faktörlerdir. Bu faktörlerin içinde en karmaşık ve belirsiz olanlar, kontrol edilemeyen meteorolojik değişkenlerdir. Bu anlamda meterolojik faktörlerdeki olası değişiklerin belirlenmesi, tarımsal üretimin gelecekteki durumu hakkında fikir sahibi olmamızı sağlayacaktır. Dünya’da, olası iklim değişikliği ve bunun tarıma etkilerini inceleyen çeşitli araştırmalar yapılmaktadır. Teknolojinin hızla geliştiği günümüz şartlarında bu araştırmalarda bitki-iklim simulasyon modelleri kullanılmaktadır. Bunlar, tarımsal sistemlerin davranışlarını analiz etmek amacıyla geliştirilen matematiksel modellerdir. Ekilen tohum sayısı, gübreleme vb tarımsal yönetim girdileri ile sıcaklık, bağıl nem, yağış, radyasyon vb. meteorolojik değişkenler modellerde girdi olarak kullanılır. Bu çalışmada amaçlanan, olası iklim değişikliği senaryolarını dikkate alarak Kırklareli’nde yetiştirilen buğday bitkisinin gelecekteki verimini araştırmaktır. Bu amaca yönelik olarak, DSSAT bitki iklim simulasyon modellerinden CERES-Wheat modeli kullanılmıştır. Modelin girdi ve çıktı verileri olarak Kırklareli Toprak Su ve Tarımsal Meteoroloji Araştırma İstasyonu Müdürlüğü arazisinde buğday tarlası üzerine kurulan meteoroloji istasyonunda kaydedilen meteorolojik ve bu arazide ölçülen, gözlenen toprak ve bitki ile ilgili veriler kullanılmıştır. Modelin kalibre edilmesinin ardından hassasiyet analizleri yapılmıştır. Kırklareli için RegCm4, ECHAM5 global iklim modellerinin çıktıları kullanılarak bölgede gelecekte buğday verimindeki değişimler model ile simule edilmiştir. Sonuçlar incelendiğinde, buğday veriminin sıcaklık artışına oldukça tepkili olduğu gözlenmiştir (T+5 simulasyonu için -%35.9). Rg ve CO2 değerlerinin verimi olumlu etkilediği belirlenmiştir. Ancak, bu durum buğday veriminde sıcaklık artışından kaynaklanan olumsuzluğu dengeleyemediği gözlenmektedir. Benzer şekilde yağış miktarındaki azalma, buğday veriminin düşmesine neden olmaktadır. Ayrıca, buğday bitkisinin dane veriminde, 2013-2040 yılı ortalama meteorolojik verilere göre, % 8; bir sonraki 30 yılın ortalama verilerine göre (2041-2070) % 12 ve daha sonraki 30 yıllık periyodun ortalama verilerine göre ise (2071-2100) % 20’ye kadar azalma modellenmiştir. Buna ilave olarak; geçmiş yıllardaki (1975-2010) verilere göre belirlenen katsayılarla model çalıştırıldığında ise, 2013-2100 yılları arasındaki ortalama meteorolojik verilere göre, verimde % 3 ile 6 arasında bir azalma belirlenmiştir.

As a main aim of many studies and discussions, the climate change is a popular phenomenon of overall agreement. According to the reports of Intergovermental Panel on Climate Change (IPCC), increases in greenhause gases released from various sources effect global average temperatures. This situation will change the world’s climate in micro, meso and macro scales. Planning the agricultural production and determining its future are very important issues from the past to the present for human life. Interactions between soil, crop and atmosphere are the most meaningful factors that influence the agricultural production. Among these factors, the most complex and undetermined factors are the uncontrollable meteorological parameters. As such, determining the variations in meteorological parametres can provide us directive ideas about the future aspect of agricultural production. There are various global researches about climate change as well as its current and possible effects on agriculture. Related to the present technological advances, crop-climate simulation models are widely used during these studies. These models are mathematical softwares developed for the analysis of the activities of agricultural systems. Agricultural management activities like seed quantity, fertilizing, etc. and meteorological parameters like temperature, humidity, solar radiation and precipitation are used as major model inputs. In this connection, main aim of this research study was to investigate the future yield of winter wheat (triticum aestivum L.) sown in the Kırklareli city of Turkey by considering possible climate change scenarios. With a 6650 km2 surface area and an agricultural area of 268311 ha, the Kırklareli city (41° 13’ N, 26° 54’ E, 203 m asl) takes part in northwestern part of Turkey-in the Thrace Region. Concordantly, winter wheat and sunflower are the main agricultural products. The CERES-Wheat Model, which is a part of the Decision Support System for Agrotechnology Transfer (DSSAT) crop-climate simulation modelling package was used as the simulation tool. Providing the World Meteorological Organisation’s (WMO) requirements, an automatic meteorological station was established on the selected winter wheat parcel in the Kırklareli Atatürk Soil Water and Agricultural Meteorology Research Station Directorate (KRK) Field. Meteorological station data together with the measurements on soil and crop have been used as model inputs and outputs. In this connection; air temperature (average, maximum and minimum), relative humidity, wind speed, wind direction, total solar radiation, photosynthetically active radiation, net radiation, soil heat flux, soil water content, soil temperature, precipitation and surface temperature have been measured directly on cultivated plants. Furthermore; plant height, biomass and leaf area index were measured at regular intervals. Also, the agricultural activities (number of planted seeds per m2, germination percentage, amount and type of fertilizer, amount and time of irrigation, etc.) performed during plant development were recorded. Meteorological measurements were recorded in 10 min, 30 min and daily intervals by a corresponding datalogger. Soil samples were analyzed in the KRK laboratory to determine the physical and chemical properties of soil. For this purpose, soil profiles were opened in the required sections of the wheat experiment field. After the model calibration process, sensitivity analysis step was taken. This was then followed by the application of the RegCm4 regional climate model outputs as the meteorological inputs of CERES-Wheat for the simulation of future wheat yield change in the aforementioned location. Analysis of the results showed that the winter wheat is expected to be considerably responsive to temperature variations by means of some major yield indicators (total biomass, grain yield and LAI). An increase of 5 ºC in temperature would cause a reduction in yield up to 79 %. Global solar radiation (Rg) and carbondioxyde (CO2) increases are expected to affect positively on wheat yield. Sensitivity analysis showed that the maximum yield increase could occur for the Rg and CO2 increase scenarios (35 %). This positive effect, however; cannot compensate the above mentioned reduction caused by the temperature. The wheat biomass showed a similar manner in grain yield, which was influenced negatively by temperature rise (-% 42 for the T + 5 ºC scenario). In addition to the sensitivity analysis, investigation of the future climatic conditions for Kırklareli was conducted in three equal time intervals; namely for the years between 2010-2040, 2041-2070 and 2071-2100, respectively. To reach this aim, additional calibration was applied using historical database to put forth the long term overall plant growth of the mean 1975-2010 season. Accordingly, a series of simulations were done to make comparisons between the long term and future yield components. Moreover, emphasize was given to the determination of future growing seasons, during which extreme meteorological conditions were expected to occur. According to these climate model predictions, the 2010-2040 growing period has been identified as one of the most arid wheat growth periods. The 2069-2070 season was estimated as the driest development period, while the 2052-2053 was determined as the wettest season for the consecutive 30 years interval (2041-2070). Following this, for the average 2071-2100 period it was modeled that the 2090-2091 season would be the driest growing period for wheat. Hottest growth periods during the consecutive 30 years periods were estimated as 2033-2034, 2069-2070 and 2098-2099, respectively. According to the Kırklareli’s long term climate data (1975-2010), any increase in temperature would affect negatively on wheat yield. Indeed, an increase of 5 ºC in temperature could cause a 35.9 % yield reduction. Similarly, reductions in precipitation caused decreases in yield, as expected. Model predictions showed that a 40 % decrease in precipitation would affect negatively on wheat yield as 9.7 %. By contrast, with the temperature, global solar radiation (Rg) and carbondioxyde (CO2) increases affected wheat yield positively. Possible Rg and CO2 senarios showed increases in grain yield up to 16.1 and 27.6 %. Model runs due to the 2013-2040 average meteorologic data indicated grain yield increases of wheat up to 8 %. The reduction keeps its trend for the succesive 30 years period as 12 and 20 % for the consequtive (30-year) period (2071-2100). Evaluation of these three different periods for the future showed that there will be reduction in wheat yield between 14 % and 64 % for the driest future growing season. Ratio of thr reduction will vary between 35 to 64 % for the hottest season. In the future; meteorological, plant, soil and agricultural activities data, which are necessary as input and/or output for models, should be recorded regularly in our country. This can enable the related researchers to use the same model or similar models for further analysis. Any model can be calibrated for different crops and different climatic conditions of countries. This will provide more accurate decisions to make investments for the future. This thesis is the first step to overcome the lack of examination of possible effects of climate change on winter wheat yield in northwestern Turkey. This thesis has been carried out under the TUBITAK project conducted by Prof. Levent ŞAYLAN. For this reason, I would like to thank TUBITAK.