This work investigates the aerodynamics of a NACA 0012 airfoil at the chord-based Reynolds numbers (Re c ) from 5.3 × 10 3 to 2.0 × 10 4 . The lift and drag coefficients, C L and C D , of the airfoil, along with the flow structure, were measured as the turbulent intensity T u of oncoming flow varies from 0.6% to 6.0%. The analysis of the present data and those in the literature unveils a total of eight distinct flow structures around the suction side of the airfoil. Four Re c regimes, i.e., the ultra-low (<1.0 × 10 4 ), low (1.0 × 10 4 -3.0 × 10 5 ), moderate (3.0 × 10 5 -5.0 × 10 6 ), and high Re c (>5.0 × 10 6 ), are proposed based on their characteristics of the C L -Re c relationship and the flow structure. It has been observed that T u has a more pronounced effect at lower Re c than at higher Re c on the shear layer separation, reattachment, transition, and formation of the separation bubble. As a result, C L , C D , C L /C D and their dependence on the airfoil angle of attack all vary with T u . So does the critical Reynolds number Re c,cr that divides the ultra-low and low Re c regimes. It is further noted that the effect of increasing T u bears similarity in many aspects to that of increasing Re c , albeit with differences. The concept of the effective Reynolds number Re c,eff advocated for the moderate and high Re c regimes is re-evaluated for the low and ultra-low Re c regimes. The Re c,eff treats the non-zero T u effect as an addition of Re c and is determined based on the presently defined Re c,cr . It has been found that all the maximum lift data from both present measurements and previous reports collapse into a single curve in the low and ultra-low Re c regimes if scaled with Re c,eff .

Exploring the dynamic evolution of the abrupt alternation between wet and dry spells in adjacent months plays a crucial role in water resources planning and agricultural development in a changing climate. The dry-wet abrupt alternation (DWAA) has been studied based on hydrometeorological observations over the past several years. However, little effort has been made to explore DWAA from a climate projection standpoint. Furthermore, few studies have investigated potential interrelationships between DWAA and heavy rainfall. In this study, the interrelationships between DWAA events and heavy rainfall with various intensities as well as potential evapotranspiration are revealed explicitly through the convection-permitting climate simulations for 10 climate divisions over Texas in the United States. Our findings disclose that the increasing heavy rainfall and potential evapotranspiration lead to more frequent occurrence of DWAA events over a larger spatial extent. Heavy rainfall with daily precipitation greater than 20 mm contributes most to the occurrence of DWAA. In addition, a severe phenomenon of dry-wet-dry alternation is projected to appear due to the increasing number of heavy rainfall and drought events as well as the deteriorated soil water holding capacity under global warming.Plain Language Summary The dry-wet abrupt alternation (DWAA) has dramatic negative impacts on water security and agricultural production. DWAA is a devastating natural disaster which is characterized by an abrupt alternation between wet and dry spells in adjacent months. Exploring the underlying mechanism and complex evolution of DWAA is thus crucial to helping policymakers and stakeholders develop sound adaptation and mitigation plans for reducing potential risks of natural extreme events. We find that the DWAA event is projected to occur simultaneously in multiple climate divisions, especially for the most populous region of South Texas. Heavy rainfall with daily precipitation greater than 20 mm contributes most to the occurrence of DWAA. Due to the increasing number of drought and heavy rainfall events, a severe super extreme event of the dry-wet-dry alternation is projected to appear by the end of this century, whereas there is no historical record on the occurrence of such an extreme event over Texas in the period of 1981-1995.

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Probabilistic projections of future drought characteristics play a crucial role in climate change adaptation and disaster risk reduction. This study presents a copula‐based probabilistic framework for projecting future changes in multivariable drought characteristics through convection‐permitting Weather Research and Forecasting simulations with 4‐km horizontal grid spacing. A probabilistic multivariate drought index is introduced to examine the joint effects of drought indicators with uncertainty intervals for four major river basins located in South Central Texas of the United States. Markov chain Monte Carlo is used to address uncertainties in assessing copula parameters and in predicting climate‐induced changes in hydrological regimes. Our findings reveal that the severity and intensity of drought episodes can be amplified when considering the compound effects of soil moisture and runoff regimes by using the probabilistic multivariate drought index. The South Central Texas region is projected to experience more drought events with shorter duration and higher intensity in a changing climate. The drought severity will not necessarily increase due to the decreasing drought duration. In addition, our findings indicate that the intensity of future droughts is expected to increase as a result of the deficiency of soil moisture even though precipitation extremes are projected to become more frequent. Moreover, climate change impacts on multivariate drought characteristics will intensify with the increasing temporal scales (i.e., short‐, medium‐, and long‐term droughts) although the number of future drought events may decrease by the end of this century.