Table 6 Key messages towards adaptation to future temperature changes in the Bărăgan Plain agricultural region

GSL

Reflects the length of the vegetative season for both indigenous and cultivated plants, when they experience the most growth, and calendars under average climatic conditions

GSL is on a notable increase under RCP4.5 and RCP8.5, from up to one week to one month and a half by the end of the 21 century. Under RCP8.5, the lengthening rates are the largest, ranging from 8 days (2021–2050) to 49 days (2071–2100).

Higher temperatures are likely to accelerate the development of cultivated plants in the study region (e.g. winter wheat) and to shorten the growth stages during which the photosynthetic products are absorbed, affecting the overall crop productivity.

ES

Provides evidence of the growing season onset for crops and is also a reliable estimator of the changes in the greening phenological phases of plants in certain years.

There is evidence of increasing frequency of earlier spring onsets, most significant changes being projected for the far-future (30 to 86 %), in all scenarios.

This is an indication of decreasing cold stress and advancing active crop vegetation season.

FU

Proxy indicator of winter severity, is a relevant indicator for assessing the cold stress influence on crops sowed during autumn, which extend their vegetation period also during the winter (e.g. winter wheat) (Sandu et al., 2010).

Under present climate, the study region is highly exposed to cold stress, generally from November to March. By 2050 (A1B), FU is on significant decrease (34 %), suggesting the transition towards milder winters. This signal is consistent with the negative changes in the annual frequency of frost days (Tmin ≤ 0 °C) under the same scenario (about 13 %), confirming the general reduction of cold stress in the region, especially in February and March, as well as the increasing rates of photosynthesis.

The milder character of winters is expected to have both positive and negative effects on crops, dependent on the their development stages. For winter wheat, warmer winters are likely to be beneficial (less cold stress on seeds), but rather detrimental during the vernalization phase (the period of cooler growing conditions necessary that winter wheat to develop the reproductive growth).

Tmin0

Tmax30

Important parameters of heat stress on plants during the active crop growth season (April-October). The 30 °C and 32 °C maximum temperature thresholds are considered critical (and even lethal) biological limits for plant development, especially for maize and sunflower crops, when producing over several consecutive days and overlapping the flowering, grain filling and ripening stages (Sandu et al., 2010).

The Bărăgan Plain is frequently affected by severe and persistent heat stress in summer, under the influence of tropical dry airflows of North-African origins. The projections indicate that the region is likely to experience a higher tropical heat stress by 2050, through an increasing frequency of tropical days in summer but also during the early-to-mid autumn interval (in September-October) mid-to-late spring (in April-May).

Tropical days and extremely hot days negatively influence the plant metabolism, producing the so-called "shrivelling" phenomena, highly detrimental to crop development when associated to summer soil moisture deficit.

Tmax32

Heat stress by means of extremely hot units index is likely to be significantly augmented by 2050 all over the region.